Archive for February, 2011

Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news. Planet 3.0 also reports new research.

Published last week:

Ocean blooming event caused by volcanic eruption

Fertilization potential of volcanic dust in the low-nutrient low-chlorophyll western North Pacific subtropical gyre: Satellite evidence and laboratory study – Lin et al. (2011)“In the western North Pacific subtropical ocean, the Anatahan volcano of the Mariana Islands erupted on 10 May 2003 for the first time in recorded history. Based on nine different types of remote sensing data provided by NASA, laboratory experiment of the Anatahan samples, and a 3-D ocean circulation model developed by the U.S. Naval Research Laboratory, the postvolcanic ocean biogeochemical response to the Anatahan eruption was explored. It was observed that soon after the eruption, the aerosol optical depth abruptly increased from the pre-eruption loading of ∼0.1 to ∼2. In the week following the eruption, a “bloom-like” patch was observed by NASA’s Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) ocean color sensor. Based on the chlorophyll a, fluorescence line height (FLH), at-sensor total radiance, and normalized water-leaving radiance data obtained by MODIS, the cause of the bloom-like patch was diagnosed. The results suggest that the patch was most likely a mixture of suspended volcanic particles and a phytoplankton bloom. FLH was found to be ∼9–17 × 10−3 mW cm−2 μm−1 sr−1 in the patch and ∼3–5 × 10−3 mW cm−2 μm−1 sr−1 in the ambient water, indicating that a 2–5-fold increase in biological activity occurred during the week following the eruption. Satellite altimetry indicated that the bloom took place in the presence of downwelling and was not a result of upwelled nutrients in this oligotrophic ocean. Analysis of satellite ocean color spectra of the bloom region found similar spectra as the reference Trichodesmium spectra. Laboratory experiments further substantiate the satellite observations which show elevated concentrations of limiting nutrients provided by the Anatahan samples, and the averaged soluble nitrate, phosphate, and Fe were 42, 3.1, and 2.0 nM, respectively. Though it was not possible to obtain in situ observations of the ocean biogeochemical responses that followed the Anatahan eruption, this study provided evidence based on remote sensing data and laboratory experiment that fertilization of volcanic aerosols occurred following this eruption in one of the most oligotrophic low-nutrient low-chlorophyll ocean deserts on Earth.” Lin, I.-I., et al. (2011), Global Biogeochem. Cycles, 25, GB1006, doi:10.1029/2009GB003758.

With climate change humans migrate to higher mountains too

Relationship between tourism demand in the Swiss Alps and hot summer air temperatures associated with climate change – Serquet & Rebetez (2011)“We quantified the impacts of hot summer air temperatures on tourism in the Swiss Alps by analysing the relationship between temperature and overnight stays in 40 Alpine resorts. Several temperature thresholds were tested to detect the relationship between them and summer tourism. Our results reveal significant correlations between the number of nights spent in mountain resorts and hot temperatures at lower elevations. The relationship between hot temperatures and overnight stays is more important in June and to a lesser extent in August than in July. This is probably because holidays and the peak of domestic tourist demand in summer usually take place between the beginning of July and mid-August so that long-term planned stays dominate more during these months compared to June. The alpine resorts nearest to cities are most affected by hot temperatures. This is probably because reactions to hot episodes take place on a short-term basis as heat waves remain relatively rare. Our results suggest that alpine tourist resorts could benefit from hotter temperatures at lower elevations under future climates. Tourists already react on a short-term basis to hot days and spend more nights in hotels in mountain resorts. If heat waves become more regular, it seems likely that tourists will choose to stay at alpine resorts more frequently and for longer periods.” G. Serquet and M. Rebetez, Climatic Change, 2011, DOI: 10.1007/s10584-010-0012-6.

MWP not analogous to modern times advancing NA glaciers suggest

Extensive glaciers in northwest North America during Medieval time – Koch & Clague (2011)“The Medieval Warm Period is an interval of purportedly warm climate during the early part of the past millennium. The duration, areal extent, and even existence of the Medieval Warm Period have been debated; in some areas the climate of this interval appears to have been affected more by changes in precipitation than in temperature. Here, we provide new evidence showing that several glaciers in western North America advanced during Medieval time and that some glaciers achieved extents similar to those at the peak of the Little Ice Age, many hundred years later. The advances cannot be reconciled with a climate similar to that of the twentieth century, which has been argued to be an analog, and likely were the result of increased winter precipitation due to prolonged La Niña-like conditions that, in turn, may be linked to elevated solar activity. Changes in solar output may initiate a response in the tropical Pacific that directly impacts the El Niño/Southern Oscillation and associated North Pacific teleconnections.” Johannes Koch and John J. Clague, Climatic Change, 2011, DOI: 10.1007/s10584-010-0016-2.

Ocean blooms right after ice retreats

Near-ubiquity of ice-edge blooms in the Arctic – Perrette et al. (2011)“Ice-edge blooms are significant features of Arctic primary production, yet have received relatively little attention. Here we combine satellite ocean colour and sea-ice data in a pan-Arctic study. Ice-edge blooms occur in all seasonally ice-covered areas and from spring to late summer, being observed in 77–89% of locations for which adequate data exist, and usually peaking within 20 days of ice retreat. They sometimes form long belts along the ice-edge (greater than 100 km), although smaller structures were also found. The bloom peak is on average more than 1 mg m−3, with major blooms more than 10 mg m−3, and is usually located close to the ice-edge, though not always. Some propagate behind the receding ice-edge over hundreds of kilometres and over several months, while others remain stationary. The strong connection between ice retreat and productivity suggests that the ongoing changes in Arctic sea-ice may have a significant impact on higher trophic levels and local fish stocks.” Perrette, M., Yool, A., Quartly, G. D., and Popova, E. E., Biogeosciences, 8, 515-524, doi:10.5194/bg-8-515-2011, 2011. [full text]

Spanish hockey stick

Land surface temperature changes in Northern Iberia since 4000 yr BP, based on δ13C of speleothems – Martín-Chivelet et al. (2011)“The surface temperature changes for the last 4000 years in northern inland Iberia (an area particularly sensitive to climate change) are determined by a high resolution study of carbon stable isotope records of stalagmites from three caves (Kaite, Cueva del Cobre, and Cueva Mayor) separated several 10 s km away in N Spain. Despite the local conditions of each cave, the isotopic series show a good overall coherence, and resulted to be strongly sensitive to surface temperature changes. The record reflects alternating warmer and colder intervals, always within a temperature range of 1.6 °C. The timing and duration of the intervals were provided by 43 230Th–234U (ICP-MS) ages. Main climatic recognized periods are: (1) 3950–3000 yr BP: warm period punctuated by cool events around ~ 3950, 3550 and 3250 yr BP; (2) 2850–2500 yr BP cold interval (Iron Age Cold Period); (3) 2500–1650 yr BP moderate warm period (Roman Warm Period), with maximum temperatures between 2150 and 1750 yr BP; (4) 1650–1350 yr BP cold interval (Dark Ages Cold Period), with a thermal minimum at ~ 1500 yr BP; (5) 1350–750 yr BP warm period (Medieval Warm Period) punctuated by two cooler events at ~ 1250 and ~ 850 yr BP; (6) 750–100 yr BP cold period (Little Ice Age) with extremes occurring at 600–500 yr BP, 350–300 yr BP, and 150–100 yr BP; and (7) the last 150 years, characterized by rapid but no linear warming (Modern Warming). Remarkably, the presented records allow direct comparison of recent warming with former warm intervals such as the Roman or the Medieval periods. That comparison reveals the 20th Century as the time with highest surface temperatures of the last 4000 years for the studied area. Spectral analysis of the time series shows consistent climatic cycles of ~ 400, ~ 900 and ~ 1300 yr, comparable with those recognized in the North Atlantic marine record, the Greenland ice cores, and other terrestrial records for the middle – late Holocene, suggesting common climate forcing mechanisms related to changes in solar irradiance and North Atlantic circulation patterns.” Javier Martín-Chivelet, M. Belén Muñoz-García, R. Lawrence Edwards, María J. Turrero, and Ana I. Ortega, Global and Planetary Change, doi:10.1016/j.gloplacha.2011.02.002.

Elephant seals measuring the ocean

Delayed-mode calibration of hydrographic data obtained from animal-borne satellite-relay data loggers – Roquet et al. (2011)“A delayed-mode calibration procedure is presented to improve the quality of hydrographic data from CTD-Satellite-Relay Data Loggers (CTD-SRDL) deployed on elephant seals. This procedure is applied on a dataset obtained with 10 CTD-SRDLs deployed at Kerguelen Islands in 2007. A comparison of CTD-SRDLs with a ship-based CTD system is first presented. A pressure effect correction, linear with pressure, is deduced for both temperature and salinity measurements. An external field effect on conductivity sensor is also detected, inducing an additional salinity offset. The salinity offset cannot be estimated directly from the ship-based CTD comparisons, as the attachment of the CTD-SRDL on the seal head modifies the magnitude of the external field effect. Two methods are proposed to estimate a posteriori the salinity offset. The first method uses the stable salinity maximum characterizing the Lower Circumpolar Deep Water (LCDW), sampled by seals foraging south of the Southern Antarctic Circumpolar Current Front. Where this approach is not possible, a statistical method of cross-comparison of CTD-SRDLs surface salinity measurements is used over the sluggish Northern Kerguelen Plateau. Accuracies are respectively estimated as ± 0.02 °C for temperature and ± 0.1 for derived salinity without corrections. The delayed-mode calibration improves significantly the CTD-SRDL data, improving accuracies to ± 0.01 °C and ± 0.03 respectively. A better salinity accuracy of ± 0.02 is achieved when the LCDW method can be used. For CTD-SRDLs where ship-based CTD comparisons are not available, the expected accuracy would be ± 0.02 °C for temperature and ± 0.04 for the derived salinity.” Fabien Roquet, Jean-Benoit Charrassin, Stephane Marchand, Lars Boehme, Mike Fedak, Gilles Reverdin and Christophe Guinet, Journal of Atmospheric and Oceanic Technology 2011.

Younger Dryas event probably not caused by impact

The Younger Dryas impact hypothesis: A requiem – Pinter et al. (2011)“The Younger Dryas (YD) impact hypothesis is a recent theory that suggests that a cometary or meteoritic body or bodies hit and/or exploded over North America 12,900 years ago, causing the YD climate episode, extinction of Pleistocene megafauna, demise of the Clovis archaeological culture, and a range of other effects. Since gaining widespread attention in 2007, substantial research has focused on testing the 12 main signatures presented as evidence of a catastrophic extraterrestrial event 12,900 years ago. Here we present a review of the impact hypothesis, including its evolution and current variants, and of efforts to test and corroborate the hypothesis. The physical evidence interpreted as signatures of an impact event can be separated into two groups. The first group consists of evidence that has been largely rejected by the scientific community and is no longer in widespread discussion, including: particle tracks in archeological chert; magnetic nodules in Pleistocene bones; impact origin of the Carolina Bays; and elevated concentrations of radioactivity, iridium, and fullerenes enriched in 3He. The second group consists of evidence that has been active in recent research and discussions: carbon spheres and elongates, magnetic grains and magnetic spherules, byproducts of catastrophic wildfire, and nanodiamonds. Over time, however, these signatures have also seen contrary evidence rather than support. Recent studies have shown that carbon spheres and elongates do not appear to represent extraterrestrial carbon nor impact-induced megafires, but rather fungal sclerotia and arthropod fecal material that are a small but common component of many terrestrial deposits. Magnetic grains and spherules are heterogeneously distributed in sediments, but reported measurements of unique peaks in concentrations at the YD onset have yet to be reproduced. The magnetic grains are certainly just iron-rich detrital grains, whereas reported YD magnetic spherules are consistent with the diffuse, non-catastrophic input of micrometeorite ablation fallout, probably augmented by anthropogenic and other terrestrial spherular grains. Results here also show considerable subjectivity in the reported sampling methods that may explain the purported YD spherule concentration peaks. Fire is a pervasive earth-surface process, and reanalyses of the original YD sites and of coeval records show episodic fire on the landscape through the latest Pleistocene, with no unique fire event at the onset of the YD. Lastly, with YD impact proponents increasingly retreating to nanodiamonds (cubic, hexagonal [lonsdaleite], and the proposed n-diamond) as evidence of impact, those data have been called into question. The presence of lonsdaleite was reported as proof of impact-related shock processes, but the evidence presented was inconsistent with lonsdaleite and consistent instead with polycrystalline aggregates of graphene and graphane mixtures that are ubiquitous in carbon forms isolated from sediments ranging from modern to pre-YD age. Important questions remain regarding the origins and distribution of other diamond forms (e.g., cubic nanodiamonds). In summary, none of the original YD impact signatures have been subsequently corroborated by independent tests. Of the 12 original lines of evidence, seven have so far proven to be non-reproducible. The remaining signatures instead seem to represent either (1) non-catastrophic mechanisms, and/or (2) terrestrial rather than extraterrestrial or impact-related sources. In all of these cases, sparse but ubiquitous materials seem to have been misreported and misinterpreted as singular peaks at the onset of the YD. Throughout the arc of this hypothesis, recognized and expected impact markers were not found, leading to proposed YD impactors and impact processes that were novel, self-contradictory, rapidly changing, and sometimes defying the laws of physics. The YD impact hypothesis provides a cautionary tale for researchers, the scientific community, the press, and the broader public.” Nicholas Pinter, Andrew C. Scott, Tyrone L. Daulton, Andrew Podoll, Christian Koeberl, R. Scott Anderson, and Scott E. Ishman, Earth-Science Reviews, 2011, doi:10.1016/j.earscirev.2011.02.005.

Measuring pollution events in real time

Continuous isotopic composition measurements of tropospheric CO2 at Jungfraujoch (3580 m a.s.l.), Switzerland: real-time observation of regional pollution events – Tuzson et al. (2011)“A quantum cascade laser based absorption spectrometer (QCLAS) is applied for the first time to perform in situ, continuous and high precision isotope ratio measurements of CO2 in the free troposphere. Time series of the three main CO2 isotopologue mixing ratios (12C16CO2, 13C16CO2 and 12C18O16O) have simultaneously been measured at one second time resolution over two years (from August 2008 to present) at the High Altitude Research Station Jungfraujoch (3580 m a.s.l., Switzerland). This work focuses on periods in February 2009 only, when sudden and pronounced enhancements in the tropospheric CO2 were observed. These short-term changes were closely correlated with variations in CO mixing ratios measured at the same site, indicating combustion related emissions as potential source. The analytical precision of 0.046‰ (at 50 s integration time) for both δ13C and δ18O and the high temporal resolution allowed the application of the Keeling plot method for source signature identification. The spatial origin of these CO2 emission sources was then determined by backward Lagrangian particle dispersion simulations.” Tuzson, B., Henne, S., Brunner, D., Steinbacher, M., Mohn, J., Buchmann, B., and Emmenegger, L., Atmos. Chem. Phys., 11, 1685-1696, doi:10.5194/acp-11-1685-2011, 2011. [full text]

Convective activity might have enhanced in tropics

Three decades of intersatellite-calibrated High-Resolution Infrared Radiation Sounder upper tropospheric water vapor – Shi & Bates (2011)“To generate a climatologically homogenized time series of the upper tropospheric water vapor (UTWV), intersatellite calibration is carried out for 3 decades of High-Resolution Infrared Radiation Sounder (HIRS) channel 12 clear-sky measurements. Because of the independence of the individual satellite’s instrument calibration, intersatellite biases exist from satellite to satellite. To minimize the expected intersatellite biases, measurement adjustments are derived from overlapping HIRS data from the equator to the poles to account for the large global temperature observation range. Examination of the intersatellite biases shows that the biases are scene temperature–dependent. Many overlapping satellites have bias variations of more than 0.5 K across the scene temperature ranges. An algorithm is developed to account for the varying biases with respect to brightness temperature. Analyses based on the intercalibrated data show that selected regions of UTWV are highly correlated with low-frequency indexes such as the Pacific Decadal Oscillation index and the Pacific and North America index, especially in the winter months. The derived upper tropospheric humidity in the central Pacific also corresponds well with the Niño 3.4 index. Thirty year trend analysis indicates an increase of upper tropospheric humidity in the equatorial tropics. The areal coverage of both high and low humidity values also increased over time. These features suggest the possibility of enhanced convective activity in the tropics.” Shi, L., and J. J. Bates (2011), J. Geophys. Res., 116, D04108, doi:10.1029/2010JD014847.

Dominant role of GHG’s in past interglacials

Individual contribution of insolation and CO2 to the interglacial climates of the past 800,000 years – Yin & Berger (2011)“The individual contributions of insolation and greenhouse gases (GHG) to the interglacial climates of the past 800,000 years are quantified through simulations with a model of intermediate complexity LOVECLIM and using the factor separation technique. The interglacials are compared in terms of their forcings and responses of surface air temperature, vegetation and sea ice. The results show that the relative magnitude of the simulated interglacials is in reasonable agreement with proxy data. GHG plays a dominant role on the variations of the annual mean temperature of both the Globe and the southern high latitudes, whereas, insolation plays a dominant role on the variations of tree fraction, precipitation and of the northern high latitude temperature and sea ice. The Mid-Brunhes Event (MBE) appears to be significant only in GHG and climate variables dominated by it. The results also show that the relative importance of GHG and insolation on the warmth intensity varies from one interglacial to another. For the warmest (MIS-9 and MIS-5) and coolest (MIS-17 and MIS-13) interglacials, GHG and insolation reinforce each other. MIS-11 (MIS-15) is a warm (cool) interglacial due to its high (low) GHG concentration, its insolation contributing to a cooling (warming). MIS-7, although with high GHG concentrations, can not be classified as a warm interglacial due to it large insolation-induced cooling. Related to these two forcings, MIS-19 appears to be the best analogue for MIS-1. In the response to insolation, the annual mean temperatures averaged over the globe and over southern high latitudes are highly linearly correlated with obliquity. However, precession becomes important in the temperature of the northern high latitudes and controls the tree fraction globally. Over the polar oceans, the response during the local winters, although the available energy is small, is larger than during the local summers due to the summer remnant effect. The sensitivity to double CO2 is the highest for the coolest interglacial.” Qiu Zhen Yin and André Berger, Climate Dynamics, 2011, DOI: 10.1007/s00382-011-1013-5.

Review on tropical cyclones and climate change

Tropical cyclones, climate change, and scientific uncertainty: what do we know, what does it mean, and what should be done? – Grossmann & Morgan (2011)“The question of whether and to what extent global warming may be changing tropical cyclone (TC) activity is of great interest to decision makers. The presence of a possible climate change signal in TC activity is difficult to detect because interannual variability necessitates analysis over longer time periods than available data allow. Projections of future TC activity are hindered by computational limitations and uncertainties about changes in regional climate, large scale patterns, and TC response. This review discusses the state of the field in terms of theory, modeling studies and data. While Atlantic TCs have recently become more intense, evidence for changes in other basins is not persuasive, and changes in the Atlantic cannot be clearly attributed to either natural variability or climate change. However, whatever the actual role of climatic change, these concerns have opened a “policy window” that, if used appropriately, could lead to improved protection against TCs.” Iris Grossmann and M. Granger Morgan, Climatic Change, 2011, DOI: 10.1007/s10584-011-0020-1.

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This is a list of papers on coral response to global warming and the ocean acidification. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

Rapid poleward range expansion of tropical reef corals in response to rising sea surface temperatures – Yamano et al. (2011)“Rising temperatures caused by climatic warming may cause poleward range shifts and/or expansions in species distribution. Tropical reef corals (hereafter corals) are some of the world’s most important species, being not only primary producers, but also habitat-forming species, and thus fundamental ecosystem modification is expected according to changes in their distribution. Although most studies of climate change effects on corals have focused on temperature-induced coral bleaching in tropical areas, poleward range shifts and/or expansions may also occur in temperate areas. We show the first large-scale evidence of the poleward range expansion of modern corals, based on 80 years of national records from the temperate areas of Japan, where century-long measurements of in situ sea-surface temperatures have shown statistically significant rises. Four major coral species categories, including two key species for reef formation in tropical areas, showed poleward range expansions since the 1930s, whereas no species demonstrated southward range shrinkage or local extinction. The speed of these expansions reached up to 14 km/year, which is far greater than that for other species. Our results, in combination with recent findings suggesting range expansions of tropical coral-reef associated organisms, strongly suggest that rapid, fundamental modifications of temperate coastal ecosystems could be in progress.” Yamano, H., K. Sugihara, and K. Nomura (2011), Geophys. Res. Lett., 38, L04601, doi:10.1029/2010GL046474.

Modeling regional coral reef responses to global warming and changes in ocean chemistry: Caribbean case study – Buddemeier et al. (2011)“Climatic change threatens the future of coral reefs in the Caribbean and the important ecosystem services they provide. We used a simulation model [Combo (“COral Mortality and Bleaching Output”)] to estimate future coral cover in the part of the eastern Caribbean impacted by a massive coral bleaching event in 2005. Combo calculates impacts of future climate change on coral reefs by combining impacts from long-term changes in average sea surface temperature (SST) and ocean acidification with impacts from episodic high temperature mortality (bleaching) events. We used mortality and heat dose data from the 2005 bleaching event to select historic temperature datasets, to use as a baseline for running Combo under different future climate scenarios and sets of assumptions. Results suggest a bleak future for coral reefs in the eastern Caribbean. For three different emissions scenarios from the Intergovernmental Panel on Climate Change (IPCC; B1, A1B, and A1FI), coral cover on most Caribbean reefs is projected to drop below 5% by the year 2035, if future mortality rates are equivalent to some of those observed in the 2005 event (50%). For a scenario where corals gain an additional 1–1.5°C of heat tolerance through a shift in the algae that live in the coral tissue, coral cover above 5% is prolonged until 2065. Additional impacts such as storms or anthropogenic damage could result in declines in coral cover even faster than those projected here. These results suggest the need to identify and preserve the locations that are likely to have a higher resiliency to bleaching to save as many remnant populations of corals as possible in the face of projected wide-spread coral loss.” R. W. Buddemeier, Diana R. Lane and J. A. Martinich, Climatic Change, DOI: 10.1007/s10584-011-0022-z. [full text]

Coral reefs may start dissolving when atmospheric CO2 doubles – Silverman et al. (2009)“Calcification rates in stony corals are expected to decline significantly in the near future due to ocean acidification. In this study we provide a global estimate of the decline in calcification of coral reefs as a result of increase in sea surface temperature and partial pressure of CO2. This estimate, unlike previously reported estimates, is based on an empirical rate law developed from field observations for gross community calcification as a function of aragonite degree of saturation (Ωarag), sea surface temperature and live coral cover. Calcification rates were calculated for more than 9,000 reef locations using model values of Ωarag and sea surface temperature at different levels of atmospheric CO2. The maps we produced show that by the time atmospheric partial pressure of CO2 will reach 560 ppm all coral reefs will cease to grow and start to dissolve.” Silverman, J., B. Lazar, L. Cao, K. Caldeira, and J. Erez (2009), Geophys. Res. Lett., 36, L05606, doi:10.1029/2008GL036282. [full text]

Climate change and coral reef bleaching: An ecological assessment of long-term impacts, recovery trends and future outlook – Baker et al. (2008)“Since the early 1980s, episodes of coral reef bleaching and mortality, due primarily to climate-induced ocean warming, have occurred almost annually in one or more of the world’s tropical or subtropical seas. Bleaching is episodic, with the most severe events typically accompanying coupled ocean–atmosphere phenomena, such as the El Niño-Southern Oscillation (ENSO), which result in sustained regional elevations of ocean temperature. Using this extended dataset (25+ years), we review the short- and long-term ecological impacts of coral bleaching on reef ecosystems, and quantitatively synthesize recovery data worldwide. Bleaching episodes have resulted in catastrophic loss of coral cover in some locations, and have changed coral community structure in many others, with a potentially critical influence on the maintenance of biodiversity in the marine tropics. Bleaching has also set the stage for other declines in reef health, such as increases in coral diseases, the breakdown of reef framework by bioeroders, and the loss of critical habitat for associated reef fishes and other biota. Secondary ecological effects, such as the concentration of predators on remnant surviving coral populations, have also accelerated the pace of decline in some areas. Although bleaching severity and recovery have been variable across all spatial scales, some reefs have experienced relatively rapid recovery from severe bleaching impacts. There has been a significant overall recovery of coral cover in the Indian Ocean, where many reefs were devastated by a single large bleaching event in 1998. In contrast, coral cover on western Atlantic reefs has generally continued to decline in response to multiple smaller bleaching events and a diverse set of chronic secondary stressors. No clear trends are apparent in the eastern Pacific, the central-southern-western Pacific or the Arabian Gulf, where some reefs are recovering and others are not. The majority of survivors and new recruits on regenerating and recovering coral reefs have originated from broadcast spawning taxa with a potential for asexual growth, relatively long distance dispersal, successful settlement, rapid growth and a capacity for framework construction. Whether or not affected reefs can continue to function as before will depend on: (1) how much coral cover is lost, and which species are locally extirpated; (2) the ability of remnant and recovering coral communities to adapt or acclimatize to higher temperatures and other climatic factors such as reductions in aragonite saturation state; (3) the changing balance between reef accumulation and bioerosion; and (4) our ability to maintain ecosystem resilience by restoring healthy levels of herbivory, macroalgal cover, and coral recruitment. Bleaching disturbances are likely to become a chronic stress in many reef areas in the coming decades, and coral communities, if they cannot recover quickly enough, are likely to be reduced to their most hardy or adaptable constituents. Some degraded reefs may already be approaching this ecological asymptote, although to date there have not been any global extinctions of individual coral species as a result of bleaching events. Since human populations inhabiting tropical coastal areas derive great value from coral reefs, the degradation of these ecosystems as a result of coral bleaching and its associated impacts is of considerable societal, as well as biological concern. Coral reef conservation strategies now recognize climate change as a principal threat, and are engaged in efforts to allocate conservation activity according to geographic-, taxonomic-, and habitat-specific priorities to maximize coral reef survival. Efforts to forecast and monitor bleaching, involving both remote sensed observations and coupled ocean–atmosphere climate models, are also underway. In addition to these efforts, attempts to minimize and mitigate bleaching impacts on reefs are immediately required. If significant reductions in greenhouse gas emissions can be achieved within the next two to three decades, maximizing coral survivorship during this time may be critical to ensuring healthy reefs can recover in the long term.” Andrew C. Baker, Peter W. Glynn, and Bernhard Riegl, Estuarine, Coastal and Shelf Science, Volume 80, Issue 4, 10 December 2008, Pages 435-471, doi:10.1016/j.ecss.2008.09.003. [full text]

Effects of climate and seawater temperature variation on coral bleaching and mortality – McClanahan et al. (2007)“Coral bleaching due to thermal and environmental stress threatens coral reefs and possibly people who rely on their resources. Here we explore patterns of coral bleaching and mortality in East Africa in 1998 and 2005 in a region where the equatorial current and the island effect of Madagascar interact to create different thermal and physicochemical environments. A variety of temperature statistics were calculated, and their relationships with the degree-heating months (DHM), a good predictor of coral bleaching, determined. Changes in coral cover were analyzed from 29 sites that span >1000 km of coastline from Kenya to the Comoros Islands. Temperature patterns are influenced by the island effect, and there are three main temperature environments based on the rise in temperature over 52 years, measures of temperature variation, and DHM. Offshore sites north of Madagascar that included the Comoros had low temperature rises, low DHM, high standard deviations (SD), and the lowest relative coral mortality. Coastal sites in Kenya had moderate temperature rises, the lowest temperature SD, high DHM, and the highest relative coral mortality. Coastal sites in the south had the highest temperature rises, moderate SD and DHM, and low relative coral mortality. Consequently, the rate of temperature rise was less important than background variation, as reflected by SD and kurtosis measures of sea surface water temperature (SST), in predicting coral survival across 1998. Coral bleaching responses to a warm-water anomaly in 2005 were also negatively related to temperature variation, but positively correlated with the speed of water flow. Separating these effects is difficult; however, both factors will be associated with current environments on the opposite sides of reefs and islands. Reefs in current shadows may represent refugia where corals acclimate and adapt to environmental variation, which better prepares them for rising temperature and anomalies, even though these sites are likely to experience the fastest rates of temperature rise. We suggest that these sites are a conservation priority and should be targeted for management and further ecological research in order to understand acclimation, adaptation, and resilience to climate change.” McClanahan, Timothy R., Mebrahtu Ateweberhan, Christopher A. Muhando, Joseph Maina, and Mohammed S. Mohammed. 2007, Ecological Monographs 77:503–525, doi:10.1890/06-1182.1. [full text]

The role of zooxanthellae in the thermal tolerance of corals: a ‘nugget of hope’ for coral reefs in an era of climate change – Berkelmans & van Oppen (2006)“The ability of coral reefs to survive the projected increases in temperature due to global warming will depend largely on the ability of corals to adapt or acclimatize to increased temperature extremes over the next few decades. Many coral species are highly sensitive to temperature stress and the number of stress (bleaching) episodes has increased in recent decades. We investigated the acclimatization potential of Acropora millepora, a common and widespread Indo-Pacific hard coral species, through transplantation and experimental manipulation. We show that adult corals, at least in some circumstances, are capable of acquiring increased thermal tolerance and that the increased tolerance is a direct result of a change in the symbiont type dominating their tissues from Symbiodinium type C to D. Our data suggest that the change in symbiont type in our experiment was due to a shuffling of existing types already present in coral tissues, not through exogenous uptake from the environment. The level of increased tolerance gained by the corals changing their dominant symbiont type to D (the most thermally resistant type known) is around 1–1.5 °C. This is the first study to show that thermal acclimatization is causally related to symbiont type and provides new insight into the ecological advantage of corals harbouring mixed algal populations. While this increase is of huge ecological significance for many coral species, in the absence of other mechanisms of thermal acclimatization/adaptation, it may not be sufficient to survive climate change under predicted sea surface temperature scenarios over the next 100 years. However, it may be enough to ‘buy time’ while greenhouse reduction measures are put in place.” Ray Berkelmans and Madeleine J.H van Oppen, Proc. R. Soc. B 22 September 2006 vol. 273 no. 1599 2305-2312, doi: 10.1098/rspb.2006.3567. [full text]

Global assessment of coral bleaching and required rates of adaptation under climate change – Donner et al. (2005)“Elevated ocean temperatures can cause coral bleaching, the loss of colour from reef-building corals because of a breakdown of the symbiosis with the dinoflagellate Symbiodinium. Recent studies have warned that global climate change could increase the frequency of coral bleaching and threaten the long-term viability of coral reefs. These assertions are based on projecting the coarse output from atmosphere–ocean general circulation models (GCMs) to the local conditions around representative coral reefs. Here, we conduct the first comprehensive global assessment of coral bleaching under climate change by adapting the NOAA Coral Reef Watch bleaching prediction method to the output of a low- and high-climate sensitivity GCM. First, we develop and test algorithms for predicting mass coral bleaching with GCM-resolution sea surface temperatures for thousands of coral reefs, using a global coral reef map and 1985–2002 bleaching prediction data. We then use the algorithms to determine the frequency of coral bleaching and required thermal adaptation by corals and their endosymbionts under two different emissions scenarios. The results indicate that bleaching could become an annual or biannual event for the vast majority of the world’s coral reefs in the next 30–50 years without an increase in thermal tolerance of 0.2–1.0°C per decade. The geographic variability in required thermal adaptation found in each model and emissions scenario suggests that coral reefs in some regions, like Micronesia and western Polynesia, may be particularly vulnerable to climate change. Advances in modelling and monitoring will refine the forecast for individual reefs, but this assessment concludes that the global prognosis is unlikely to change without an accelerated effort to stabilize atmospheric greenhouse gas concentrations.” Simon D. Donner, William J. Skirving, Christopher M. Little, Michael Oppenheimer, Ove Hoegh-Guldberg, Global Change Biology, Volume 11, Issue 12, pages 2251–2265, December 2005. [full text]

Coral reefs: Corals’ adaptive response to climate change – Baker et al. (2004)“The long-term response of coral reefs to climate change depends on the ability of reef-building coral symbioses to adapt or acclimatize to warmer temperatures, but there has been no direct evidence that such a response can occur. Here we show that corals containing unusual algal symbionts that are thermally tolerant and commonly associated with high-temperature environments are much more abundant on reefs that have been severely affected by recent climate change. This adaptive shift in symbiont communities indicates that these devastated reefs could be more resistant to future thermal stress, resulting in significantly longer extinction times for surviving corals than had been previously assumed.” Andrew C. Baker, Craig J. Starger, Tim R. McClanahan & Peter W. Glynn, Nature 430, 741 (12 August 2004) | doi:10.1038/430741a. [full text]

Coral reef calcification and climate change: The effect of ocean warming – McNeil et al. (2004)“Coral reefs are constructed of calcium carbonate (CaCO3). Deposition of CaCO3 (calcification) by corals and other reef organisms is controlled by the saturation state of CaCO3 in seawater (Ω) and sea surface temperature (SST). Previous studies have neglected the effects of ocean warming in predicting future coral reef calcification rates. In this study we take into account both these effects by combining empirical relationships between coral calcification rate and Ω and SST with output from a climate model to predict changes in coral reef calcification rates. Our analysis suggests that annual average coral reef calcification rate will increase with future ocean warming and eventually exceed pre-industrial rates by about 35% by 2100. Our results suggest that present coral reef calcification rates are equivalent to levels in the late 19th century and does not support previous suggestions of large and potentially catastrophic decreases in the future.” McNeil, B. I., R. J. Matear, and D. J. Barnes (2004), Geophys. Res. Lett., 31, L22309, doi:10.1029/2004GL021541. [full text, comment by Kleypas et al., reply by McNeil et al.]

Global Trajectories of the Long-Term Decline of Coral Reef Ecosystems – Pandolfi et al. (2003)“Degradation of coral reef ecosystems began centuries ago, but there is no global summary of the magnitude of change. We compiled records, extending back thousands of years, of the status and trends of seven major guilds of carnivores, herbivores, and architectural species from 14 regions. Large animals declined before small animals and architectural species, and Atlantic reefs declined before reefs in the Red Sea and Australia, but the trajectories of decline were markedly similar worldwide. All reefs were substantially degraded long before outbreaks of coral disease and bleaching. Regardless of these new threats, reefs will not survive without immediate protection from human exploitation over large spatial scales.” John M. Pandolfi, Roger H. Bradbury, Enric Sala, Terence P. Hughes, Karen A. Bjorndal, Richard G. Cooke, Deborah McArdle, Loren McClenachan, Marah J. H. Newman, Gustavo Paredes, Robert R. Warner and Jeremy B. C. Jackson, Science 15 August 2003: Vol. 301 no. 5635 pp. 955-958, DOI: 10.1126/science.1085706.

Microbial diseases of corals and global warming – Rosenberg & Haim (2002)“Coral bleaching and other diseases of corals have increased dramatically during the last few decades. As outbreaks of these diseases are highly correlated with increased sea-water temperature, one of the consequences of global warming will probably be mass destruction of coral reefs. The causative agent(s) of a few of these diseases have been reported: bleaching of Oculina patagonica by Vibrio shiloi; black band disease by a microbial consortium; sea-fan disease (aspergillosis) by Aspergillus sydowii; and coral white plague possibly by Sphingomonas sp. In addition, we have recently discovered that Vibrio coralyticus is the aetiological agent for bleaching the coral Pocillopora damicornis in the Red Sea. In the case of coral bleaching by V. shiloi, the major effect of increasing temperature is the expression of virulence genes by the pathogen. At high summer sea-water temperatures, V. shiloi produces an adhesin that allows it to adhere to a β-galactoside-containing receptor in the coral mucus, penetrate into the coral epidermis, multiply intracellularly, differentiate into a viable-but-not-culturable (VBNC) state and produce toxins that inhibit photosynthesis and lyse the symbiotic zooxanthellae. In black band disease, sulphide is produced at the coral–microbial biofilm interface, which is probably responsible for tissue death. Reports of newly emerging coral diseases and the lack of epidemiological and biochemical information on the known diseases indicate that this will become a fertile area of research in the interface between microbial ecology and infectious disease.” Eugene Rosenberg, Yael Ben-Haim, Environmental Microbiology, Volume 4, Issue 6, pages 318–326, June 2002, DOI: 10.1046/j.1462-2920.2002.00302.x. [full text]

The future of coral reefs – Knowlton (2001)“Coral reefs, with their millions of species, have changed profoundly because of the effects of people, and will continue to do so for the foreseeable future. Reefs are subject to many of the same processes that affect other human-dominated ecosystems, but some special features merit emphasis: (i) Many dominant reef builders spawn eggs and sperm into the water column, where fertilization occurs. They are thus particularly vulnerable to Allee effects, including potential extinction associated with chronic reproductive failure. (ii) The corals likely to be most resistant to the effects of habitat degradation are small, short-lived “weedy” corals that have limited dispersal capabilities at the larval stage. Habitat degradation, together with habitat fragmentation, will therefore lead to the establishment of genetically isolated clusters of inbreeding corals. (iii) Increases in average sea temperatures by as little as 1°C, a likely result of global climate change, can cause coral “bleaching” (the breakdown of coral–algal symbiosis), changes in symbiont communities, and coral death. (iv) The activities of people near reefs increase both fishing pressure and nutrient inputs. In general, these processes favor more rapidly growing competitors, often fleshy seaweeds, and may also result in explosions of predator populations. (v) Combinations of stress appear to be associated with threshold responses and ecological surprises, including devastating pathogen outbreaks. (vi) The fossil record suggests that corals as a group are more likely to suffer extinctions than some of the groups that associate with them, whose habitat requirements may be less stringent.” Nancy Knowlton, PNAS May 8, 2001 vol. 98 no. 10 5419-5425, doi: 10.1073/pnas.091092998. [full text]

Coral bleaching: the winners and the losers – Loya et al. (2001)“Sea surface temperatures were warmer throughout 1998 at Sesoko Island, Japan, than in the 10 preceding years. Temperatures peaked at 2.8 °C above average, resulting in extensive coral bleaching and subsequent coral mortality. Using random quadrat surveys, we quantitatively documented the coral community structure one year before and one year after the bleaching event. The 1998 bleaching event reduced coral species richness by 61% and reduced coral cover by 85%. Colony morphology affected bleaching vulnerability and subsequent coral mortality. Finely branched corals were most susceptible, while massive and encrusting colonies survived. Most heavily impacted were the branched Acropora and pocilloporid corals, some of which showed local extinction. We suggest two hypotheses whose synergistic effect may partially explain observed mortality patterns (i.e. preferential survival of thick-tissued species, and shape-dependent differences in colony mass-transfer efficiency). A community-structural shift occurred on Okinawan reefs, resulting in an increase in the relative abundance of massive and encrusting coral species.” Loya, Sakai, Yamazato, Nakano, Sambali, Van Woesik, Ecology Letters, Volume 4, Issue 2, pages 122–131, March 2001, DOI: 10.1046/j.1461-0248.2001.00203.x.

Climate change, coral bleaching and the future of the world’s coral reefs – Hoegh-Guldberg (1999)“Sea temperatures in many tropical regions have increased by almost 1°C over the past 100 years, and are currently increasing at ~1–2°C per century. Coral bleaching occurs when the thermal tolerance of corals and their photosynthetic symbionts (zooxanthellae) is exceeded. Mass coral bleaching has occurred in association with episodes of elevated sea temperatures over the past 20 years and involves the loss of the zooxanthellae following chronic photoinhibition. Mass bleaching has resulted in significant losses of live coral in many parts of the world. This paper considers the biochemical, physiological and ecological perspectives of coral bleaching. It also uses the outputs of four runs from three models of global climate change which simulate changes in sea temperature and hence how the frequency and intensity of bleaching events will change over the next 100 years. The results suggest that the thermal tolerances of reef-building corals are likely to be exceeded every year within the next few decades. Events as severe as the 1998 event, the worst on record, are likely to become commonplace within 20 years. Most information suggests that the capacity for acclimation by corals has already been exceeded, and that adaptation will be too slow to avert a decline in the quality of the world’s reefs. The rapidity of the changes that are predicted indicates a major problem for tropical marine ecosystems and suggests that unrestrained warming cannot occur without the loss and degradation of coral reefs on a global scale.” Ove Hoegh-Guldberg, Marine and Freshwater Research 50(8) 839 – 866, doi:10.1071/MF99078. [full text]

The Significance of Emerging Diseases in the Tropical Coral Reef Ecosystem – Hayes & Goreau (1998)“Novel pathologies of coral reef organisms, especially reef frame building scleractinian corals, have escalated during the decade between 1987 and 1997. These emerging diseases have appeared with progressively greater frequency and over wider distribution, and have revealed more diversified characteristics than ever before. The causes of most of these infections are not yet confirmed, but they evidence a gradual decline in the vital status of the coral reef ecosystem. As specific causes are identified for these afflictions, terminology will shift from non-specific descriptions, such as “white band”, “white plague”, “white pox”, “yellow band” and “black band” diseases, to etiological and pathognomonic characterizations (e.g. aspergillosis and cyanobacteriosis). Stony corals are vulnerable to sedimentation, nutrient overloading, and chemical pollution from agricultural, urban, and domestic sources. They are incapable of relocation to other sites or of self-protection from cumulative effects of exposure to nitrates, phosphates, herbicides, pesticides, and raw sewage. In contrast to stresses attributed to warm water seasonal anomalies (e.g. coral reef bleaching), stresses imparted by pathogenic micro-organisms occur throughout the calendar year, fluctuate with changing temperature, and invariably result in tissue mortality. The coral has several mechanisms for defense. The epidermis, especially in tentacles of the coral polyp, contains nematocysts which are released in response to predators. The epidermal cells also possess cilia and a flagellary apparatus which are responsible for generating microcurrents in boundary water adjacent to the organism. These currents facilitate the entry of food into the coelenteron for digestion. Mesenterial filaments extend through the epidermis, sweep the surface of the colony, initiate digestion of food particles, and eventually return to the coelenteron. Both the epidermis and the gastrodermis contain mucocytes (or “immunocytes”) which release a mucous secretion. That mucous blanket physically insulates the tissue from particulates or soluble toxins, and may also be bacteriostatic because of immunoglobulin (IgA). The recent emergence of diseases in corals may be interpreted as the consequence of (1) changing coastal ocean water quality favoring the proliferation, attachment and colonization of microbes, and (2) reduced efficiency of the coral’s normal defenses. In order to appreciate these changes, research efforts to evaluate the microbial content of reef waters and to analyze the respective roles of mucus, cilia and flagella, and nematocysts of the corals are necessary. In this study, we have begun to detail the structural, physiological, chemical, and immunological attributes of the coral. Our analysis suggests that at least some of the emerging coral diseases may be explained by a decline in the capacity of coral colonies to mount effective protection against the increasing prevalence and varied invasive strategies of marine pathogens.” Raymond L. Hayes and Nora I. Goreau, Revista Biol Trop 46: 173–185. [full text is available in the abstract page]

Coral bleaching: causes and consequences – Brown (1997)“It has been over 10 years since the phenomenon of extensive coral bleaching was first described. In most cases bleaching has been attributed to elevated temperature, but other instances involving high solar irradiance, and sometimes disease, have also been documented. It is timely, in view of our concern about worldwide reef condition, to review knowledge of physical and biological factors involved in bleaching, the mechanisms of zooxanthellae and pigment loss, and the ecological consequences for coral communities. Here we evaluate recently acquired data on temperature and irradiance-induced bleaching, including long-term data sets which suggest that repeated bleaching events may be the consequence of a steadily rising background sea temperature that will in the future expose corals to an increasingly hostile environment. Cellular mechanisms of bleaching involve a variety of processes that include the degeneration of zooxanthellae in situ, release of zooxanthellae from mesenterial filaments and release of algae within host cells which become detached from the endoderm. Photo-protective defences (particularly carotenoid pigments) in zooxanthellae are likely to play an important role in limiting the bleaching response which is probably elicited by a combination of elevated temperature and irradiance in the field. The ability of corals to respond adaptively to recurrent bleaching episodes is not known, but preliminary evidence suggests that phenotypic responses of both corals and zooxanthellae may be significant.” B. E. Brown, Coral Reefs, Volume 16, Supplement 1, S129-S138, DOI: 10.1007/s003380050249. [full text]

Tracking South Pacific Coral Reef Bleaching
by Satellite and Field Observations – Goreau et al. (1997)“South Pacific waters with anomalously high surface temperature were tracked by satellite to identify potential sites for field study of coral reef bleaching. Areas with warm season monthly anomalies exceeding +0.9 degrees C were verified to have coral bleaching by local observers, while other areas were not affected. Comparison of 15 environmental variables, measured at 19 field sites across the area affected in 1994, shows that bleaching correlates significantly only with anomalously high temperature. Live coral cover was inversely correlated with many human population density-dependent stresses, but these were not correlated to bleaching. Observations in the Indian and Atlantic Oceans also show that coral reefs worldwide are acclimated close to their upper temperature limits and probably unable to adapt rapidly to a +1 degree C anomalous warming during the warm season.” T. J. Goreau, R. L. Hayes, and A. E. Strong, Proceedings of the 8th International Coral Reef Symposium 2:1491-1494, 1997. [full text is available in the abstract page]

Periodic mass-bleaching and elevated sea temperatures: bleaching of outer reef slope communities in Moorea, French Polynesia – Hoegh-Guldberg & Salvat (1995)“Mass-bleaching events (in which corals and other symbiotic invertebrates lose their zooxanthellae) have been occurring every 3 to 4 yr since 1979. The last report of widespread mass-bleaching in the Pacific (which included bleaching around French Polynesia) was in February-April 1991. This paper reports on mass-bleaching along the outer reef slope of Moorea, French Polynesia, in April 1994. Mass-bleaching was extensive at all sites visited, with corals being bleached down to 25 m. Colour loss by corals was due to low areal densities of zooxanthellae and the percentage of live coral affected ranged between 39.6 (+/- 7.12, SEM) (NW sites) and 72.4 (+/- 7.11, SEM) (NE sites). Bleaching also varied as a function of depth and included a wide range of species. Acropora spp. showed the most severe bleaching (89.0 to 100% of all colonies completely bleached) and Porites spp. showed the least amount of bleaching (12.9 to 42.5% of all colonies partly bleached). Pocillopora spp. showed intermediate bleaching (73.9 to 92.1% of all colonies either partly or completely bleached). The results of this report indicate that current bleaching is on a scale equal to that of the 1991 bleaching event. Temperatures recorded hourly at 14 m off the outer reef slope from July 1991 to August 1994 (and those from satellite sea surface temperature readings) indicate unusually warm sea temperatures in March 1994, which were approximately 1.0*C higher than the highest temperatures recorded in 1992 and 1993, years in which bleaching on a massive scale did not occur. The appearance of warmer temperatures preceded the onset of bleaching by 2 to 3 wk, which strongly confirms the hypothesis that positive thermal anomalies are responsible for recent bleaching events in the Central and Western Pacific.” Hoegh-Guldberg O, Salvat B, MEPS 121:181-190 (1995), doi:10.3354/meps121181.

Catastrophes, Phase Shifts, and Large-Scale Degradation of a Caribbean Coral Reef – Hughes (1994)“Many coral reefs have been degraded over the past two to three decades through a combination of human and natural disturbances. In Jamaica, the effects of overfishing, hurricane damage, and disease have combined to destroy most corals, whose abundance has declined from more than 50 percent in the late 1970s to less than 5 percent today. A dramatic phase shift has occurred, producing a system dominated by fleshy macroalgae (more than 90 percent cover). Immediate implementation of management procedures is necessary to avoid further catastrophic damage.” Terence P. Hughes, Science 9 September 1994: Vol. 265 no. 5178 pp. 1547-1551, DOI: 10.1126/science.265.5178.1547. [full text]

Coral reef bleaching: ecological perspectives – Glynn (1993)“Coral reef bleaching, the whitening of diverse invertebrate taxa, results from the loss of symbiotic zooxanthellae and/or a reduction in photosynthetic pigment concentrations in zooxanthellae residing within the gastrodermal tissues of host animals. Of particular concern are the consequences of bleaching of large numbers of reef-building scleractinian corals and hydrocorals. Published records of coral reef bleaching events from 1870 to the present suggest that the frequency (60 major events from 1979 to 1990), scale (co-occurrence in many coral reef regions and often over the bathymetric depth range of corals) and severity (>95% mortality in some areas) of recent bleaching disturbances are unprecedented in the scientific literature. The causes of small scale, isolated bleaching events can often be explained by particular stressors (e.g., temperature, salinity, light, sedimentation, aerial exposure and pollutants), but attempts to explain large scale bleaching events in terms of possible global change (e.g., greenhouse warming, increased UV radiation flux, deteriorating ecosystem health, or some combination of the above) have not been convincing. Attempts to relate the severity and extent of large scale coral reef bleaching events to particular causes have been hampered by a lack of (a) standardized methods to assess bleaching and (b) continuous, long-term data bases of environmental conditions over the periods of interest. An effort must be made to understand the impact of bleaching on the remainder of the reef community and the long-term effects on competition, predation, symbioses, bioerosion and substrate condition, all factors that can influence coral recruitment and reef recovery. If projected rates of sea warming are realized by mid to late AD 2000, i.e. a 2°C increase in high latitude coral seas, the upper thermal tolerance limits of many reef-building corals could be exceeded. Present evidence suggests that many corals would be unable to adapt physiologically or genetically to such marked and rapid temperature increases.” P. W. Glynn, Coral Reefs, Volume 12, Number 1, 1-17, DOI: 10.1007/BF00303779.

Effects of disturbance on coral communities: bleaching in Moorea, French Polynesia – Gleason (1993)“This study examines patterns of susceptibility and short-term recovery of corals from bleaching. A mass coral bleaching event began in March, 1991 on reefs in Moorea, French Polynesia and affected corals on the shallow barrier reef and to >20 m depth on the outer forereef slope. There were significant differences in the effect of the bleaching among common coral genera, with Acropora, Montastrea, Montipora, and Pocillopora more affected than Porites, Pavona, leptastrea or Millepora. Individual colonies of the common species of Acropora and Pocillopora were marked and their fate assessed on a subsequent survey in August, 1991 to determine rates of recovery and mortality. Ninety-six percent of Acropora spp. showed some degree of bleaching compared to 76% of Pocillopora spp. From March to August mortality of bleached colonies of Pocillopora was 17%, 38% recovered completely, and many suffered some partial mortality of the tissue. In contrast, 63% of the Acropora spp. died, and about 10% recovered completely. Generally, those colonies with less than 50% of the colony area affected by the bleaching recovered at a higher rate than did those with more severe bleaching. Changes in community composition four months after the event began included a significant decrease only in crustose algae and an increase in cover of filamentous algae, much of which occupied plate-like and branching corals that had died in the bleaching event. Total coral cover and cover of susceptible coral genera had declined, but not significantly, after the event.” M. G. Gleason, Coral Reefs, Volume 12, Numbers 3-4, 193-201, DOI: 10.1007/BF00334479.

An Assessment of Global Warming Stress on Caribbean Coral Reef Ecosystems – Atwood et al. (1992)“There is evidence that stress on coral reef ecosystems in the Caribbean region is increasing. Recently numerous authors have stated that the major stress results from “abnormally high” seasonal sea surface temperatures (SST) and have implicated global warming as a cause, stating that recent episodes of coral bleaching result therefrom. However, an analysis of available SST data sets shows no discernible warming trend that could cause an increase in coral bleaching. Given the lack of long-term records synoptic with observations of coral ecosystem health, there is insufficient evidence available to label temperatures observed in coincidence with recent regional bleaching events as “abnormally” high.” Atwood, Donald K.; Hendee, James C.; Mendez, Antonio, Bulletin of Marine Science, Volume 51, Number 1, July 1992 , pp. 118-130(13).

Coral reef bleaching in the 1980s and possible connections with global warming – Glynn (1991)“Scleractinian corals and their symbiotic dinoflagellate algae build massive, wave-resistant coral reefs that are pre-eminent in shallow tropical seas. This mutualism is especially sensitive to numerous environmental stresses, and has been disrupted frequently during the past decade. Increased seawater temperatures have been proposed as the most likely cause of coral reef bleaching, and it has been suggested that the recent large-scale disturbances are the first biological indication of global warming. This article describes recent bleaching events and their possible link with sea warming and other environmental stresses, and offers some speculation on the fate of coral reefs if the Earth enters a sustained period of warming.” Peter W. Glynn, Trends in Ecology & Evolution, Volume 6, Issue 6, June 1991, Pages 175-179, doi:10.1016/0169-5347(91)90208-F.

Damage and recovery of coral reefs affected by El Niño related seawater warming in the Thousand Islands, Indonesia – Brown & Suharsono (1990)“Extensive coral bleaching occurred during sea-water warming (as a result of the 1982/3 El Niño Southern Oscillation event) in 1983 on the shallow reefs in the Java Sea. Mean seawater temperatures rose by 2–3° C over a six month period with values greater than 33° C being recorded between 1200–1500 h. As many as 80–90% of corals died on the reef flats at the study sites, with the major casualties being branching species in the genera Acropora and Pocillopora. Five years after the event the community structure of the study sites has recovered significantly, though coral cover is still 50% of its former level. Contrasting patterns of recovery at two selected sites, in close proximity to each other, are discussed.” B. E. Brown and Suharsono, Coral Reefs, Volume 8, Number 4, 163-170, DOI: 10.1007/BF00265007.

Widespread Coral Mortality and the 1982–83 El Niño Warming Event – Glynn (1984)“The massive ‘bleaching’ (loss of zooxanthellae) and death of reef corals that occurred in one area (Gulf of Chiriquí) on the Pacific side of Panamá and in the Galápagos Islands during February—April 1983 continued in these areas until September—October 1983, resulting in a catastrophic disturbance. Similar episodes have been reported subsequently throughout much of the tropical eastern Pacific region (Costa Rica, the entire Pacific coast of Panamá, and Colombia), in the central and western Pacific Ocean, in parts of the western Atlantic Ocean (Caribbean coasts of Costa Rica, Panamá, and Colombia), and in the Florida Keys and Bahama Islands.” Peter W. Glynn, Environmental Conservation (1984), 11: 133-146, DOI: 10.1017/S0376892900013825.

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Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news. Planet 3.0 also reports new research.

Published last week:

Anthropogenic ocean acidification shows in Bering Sea

Coupling primary production and terrestrial runoff to ocean acidification and carbonate mineral suppression in the eastern Bering Sea – Mathis et al. (2011)“Water column pH and carbonate mineral saturation states were calculated from dissolved inorganic carbon (DIC) and total alkalinity data collected over the eastern Bering Sea shelf in the spring and summer of 2008. The saturation states (Ω) of the two most important carbonate minerals, calcite (Ωcalcite) and aragonite (Ωaragonite) were strongly coupled to terrestrial runoff from the Yukon and Kuskokwim rivers, primary production in the surface waters, and remineralization of organic matter at depth over the shelf. In spring, before ice melt occurred, pH over the shelf was largely confined to a range of 7.9–8.1 and Ωcalcite and Ωaragonite ranged from 1.5 to 3.0 and 0.8 to 2.0, respectively. At the stations closest to river outflows, aragonite was undersaturated in the water column from the surface to the bottom. During the summer sea ice retreat, high rates of primary production consumed DIC in the mixed layer, which increased pH and Ωcalcite and Ωaragonite. However, Ωcalcite and Ωaragonite decreased by ∼0.3 in the bottom waters over the middle and outer shelf. Over the northern shelf, where export production is highest, Ωaragonite decreased by ∼0.35 and became highly undersaturated. The observed suppression and undersaturation of Ωcalcite and Ωaragonite in the eastern Bering Sea are correlated with anthropogenic carbon dioxide uptake into the ocean and will likely be exacerbated under business-as-usual emission scenarios. Therefore, ocean acidification could threaten some benthic and pelagic calcifying organisms across the Bering Sea shelf in the coming decades.” Mathis, J. T., J. N. Cross, and N. R. Bates (2011), Coupling primary production and terrestrial runoff to ocean acidification and carbonate mineral suppression in the eastern Bering Sea, J. Geophys. Res., 116, C02030, doi:10.1029/2010JC006453. [full text]

New estimate shows ocean’s biological carbon pump weaker

A reduced estimate of the strength of the ocean’s biological carbon pump – Henson et al. (2011)“A major term in the global carbon cycle is the ocean’s biological carbon pump which is dominated by sinking of small organic particles from the surface ocean to its interior. Several different approaches to estimating the magnitude of the pump have been used, yielding a large range of estimates. Here, we use an alternative methodology, a thorium isotope tracer, that provides direct estimates of particulate organic carbon export. A large database of thorium-derived export measurements was compiled and extrapolated to the global scale by correlation with satellite sea surface temperature fields. Our estimates of export efficiency are significantly lower than those derived from the f-ratio, and we estimate global integrated carbon export as ∼5 GtC yr−1, lower than most current estimates. The lack of consensus amongst different methodologies on the strength of the biological carbon pump emphasises that our knowledge of a major planetary carbon flux remains incomplete.” Henson, S. A., R. Sanders, E. Madsen, P. J. Morris, F. Le Moigne, and G. D. Quartly (2011), Geophys. Res. Lett., 38, L04606, doi:10.1029/2011GL046735. [full text]

Debate on prehistoric land use effects continues

Modelling prehistoric land use and carbon budgets: A critical review – Boyle et al. (2011)“An evaluation of modelled estimates for C release following early land clearance at the global level based on new model assumptions suggests that earlier studies may have underestimated its magnitude, chiefly because of underestimation of the mid-Holocene global population. Alternative information sources for population and land utilisation support both a greater total CO2 release and a greater Neolithic contribution. Indeed, we show that the quantity of terrestrial C release due to early farming, even using the most conservative assumptions, greatly exceeds the net terrestrial C release estimated by inverse modelling of ice core data by Elsig et al. (Elsig J, Schmitt J, Leuenberger D, Schneider R, Eyer M, Leuenberger M et al. (2009) Stable isotope constraints on Holocene carbon cycle changes from an Antarctic ice core. Nature 461: 507–510), though uncertainty about past global population estimates precludes calculation of a precise value.” John F. Boyle, Marie-José Gaillard, Jed O. Kaplan, John A. Dearing, The Holocene February 17, 2011, doi: 10.1177/0959683610386984.

Tropical corals in Japan expanding polewards 14 km/year

Rapid poleward range expansion of tropical reef corals in response to rising sea surface temperatures – Yamano et al. (2011)“Rising temperatures caused by climatic warming may cause poleward range shifts and/or expansions in species distribution. Tropical reef corals (hereafter corals) are some of the world’s most important species, being not only primary producers, but also habitat-forming species, and thus fundamental ecosystem modification is expected according to changes in their distribution. Although most studies of climate change effects on corals have focused on temperature-induced coral bleaching in tropical areas, poleward range shifts and/or expansions may also occur in temperate areas. We show the first large-scale evidence of the poleward range expansion of modern corals, based on 80 years of national records from the temperate areas of Japan, where century-long measurements of in situ sea-surface temperatures have shown statistically significant rises. Four major coral species categories, including two key species for reef formation in tropical areas, showed poleward range expansions since the 1930s, whereas no species demonstrated southward range shrinkage or local extinction. The speed of these expansions reached up to 14 km/year, which is far greater than that for other species. Our results, in combination with recent findings suggesting range expansions of tropical coral-reef associated organisms, strongly suggest that rapid, fundamental modifications of temperate coastal ecosystems could be in progress.” Yamano, H., K. Sugihara, and K. Nomura (2011), Geophys. Res. Lett., 38, L04601, doi:10.1029/2010GL046474.

Methane concentration might be rising again

Global column-averaged methane mixing ratios from 2003 to 2009 as derived from SCIAMACHY: Trends and variability – Frankenberg et al. (2011)“After a decade of stable or slightly decreasing global methane concentrations, ground-based in situ data show that CH4 began increasing again in 2007 and that this increase continued through 2009. So far, space-based retrievals sensitive to the lower troposphere in the time period under consideration have not been available. Here we report a long-term data set of column-averaged methane mixing ratios retrieved from spectra of the Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) instrument onboard Envisat. The retrieval quality after 2005 was severely affected by degrading detector pixels within the methane 2ν3 absorption band. We identified the most crucial problems in SCIAMACHY detector degradation and overcame the problem by applying a strict pixel mask as well as a new dark current characterization. Even though retrieval precision after the end of 2005 is invariably degraded, consistent methane retrievals from 2003 through 2009 are now possible. Regional time series in the Sahara, Australia, tropical Africa, South America, and Asia show the methane increase in 2007–2009, but we cannot yet draw a firm conclusion concerning the origin of the increase. Tropical Africa even seems to exhibit a negative anomaly in 2006, but an impact from changes in SCIAMACHY detector degradation cannot be excluded yet. Over Assakrem, Algeria, we observed strong similarities between SCIAMACHY measurements and ground-based data in deseasonalized time series. We further show long-term SCIAMACHY xCH4 averages at high spatial resolution that provide further insight into methane variations on regional scales. The Red Basin in China exhibits, on average, the highest methane abundance worldwide, while other localized features such as the Sudd wetlands in southern Sudan can also be identified in SCIAMACHY xCH4 averages.” Frankenberg, C., I. Aben, P. Bergamaschi, E. J. Dlugokencky, R. van Hees, S. Houweling, P. van der Meer, R. Snel, and P. Tol (2011), J. Geophys. Res., 116, D04302, doi:10.1029/2010JD014849.

A forest changes its CO2 exchange with climate variability

Relationships between large-scale circulation patterns and carbon dioxide exchange by a deciduous forest – Zhang et al. (2011)“In this study, we focus on a deciduous forest in central Massachusetts and investigate the relationships between global climate indices and CO2 exchange using eddy-covariance flux measurements from 1992 to 2007. Results suggest that large-scale circulation patterns influence the annual CO2 exchange in the forest through their effects on the local surface climate. Annual gross ecosystem exchange (GEE) in the forest is closely associated with spring El Niño–Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO), previous fall Atlantic Multidecadal Oscillation (AMO), and previous winter East Pacific–North Pacific (EP-NP) pattern. Annual net ecosystem exchange (NEE) responds to previous fall AMO and PDO, while annual respiration (R) is impacted by previous fall ENSO and Pacific/North American Oscillation (PNA). Regressions based on these relationships are developed to simulate the annual GEE, NEE, and R. To avoid problems of multicollinearity, we compute a “Composite Index for GEE (CIGEE)” based on a linear combination of spring ENSO and PDO, fall AMO, and winter EP-NP and a “Composite Index for R (CIR)” based on a linear combination of fall ENSO and PNA. CIGEE, CIR, and fall AMO and PDO can explain 41, 27, and 40% of the variance of the annual GEE, R, and NEE, respectively. We further apply the methodology to two other northern midlatitude forests and find that interannual variabilities in NEE of the two forests are largely controlled by large-scale circulation patterns. This study suggests that global climate indices provide the potential for predicting CO2 exchange variability in the northern midlatitude forests.” Zhang, J., L. Wu, G. Huang, and M. Notaro (2011), J. Geophys. Res., 116, D04102, doi:10.1029/2010JD014738.

Not much long-term trend in El Niño according to new reanalysis

El Niño variability in simple ocean data assimilation (SODA), 1871–2008 – Giese & Ray (2011)“A new ocean reanalysis that covers the period from 1871 to 2008 is used to explore the time-evolving characteristics of El Niño. The new reanalysis assimilates all available hydrographic and sea surface temperature data into a model of the global ocean forced with surface boundary conditions from an atmospheric reanalysis that also covers the period from 1871 through 2008. Using traditional measures of El Niño, our reanalysis shows that the timing of El Niño events is in agreement with sea surface temperature reconstructions, but El Niño in the reanalysis is stronger, particularly from 1871 to 1920. A new index based on the first moment of the temperature anomaly is introduced. The new index is used to characterize the strength and location of El Niño events and has the advantage that it is independent of the location of El Niño. Using the new index, El Niño in the reanalysis shows prominent decadal variability of strength but relatively little long-term trend. El Niño events were strong in the last part of the 19th century and first part of the 20th century and again in the latter part of the 20th century, with weak El Niño events in the middle of the 20th century. The location of El Niño also varies considerably, ranging from the western to the eastern Pacific near the coast of South America. However, the null hypothesis that the location of El Niño can be represented as a random distribution about a central longitude of about 140°W cannot be rejected.” Giese, B. S., and S. Ray (2011), J. Geophys. Res., 116, C02024, doi:10.1029/2010JC006695.

Changes in global-mean precipitation in response to warming, greenhouse gas forcing and black carbon – Frieler et al. (2011)“Precipitation changes are a key driver of climate change impacts. On average, global precipitation is expected to increase with warming. However, model projections show that precipitation does not scale linearly with surface air temperature. Instead, global hydrological sensitivity, the relative change of global-mean precipitation per degree of global warming, seems to vary across different scenarios and even with time. Based on output from 20 coupled Atmosphere-Ocean-General-Circulation-Models for up to 7 different scenarios, we discuss to what extent these variations can be explained by changes in the tropospheric energy budget. Our analysis supports earlier findings that long- and shortwave absorbers initially decrease global-mean precipitation. Including these absorbers into a multivariate scaling approach allows to closely reproduce the simulated global-mean precipitation changes. We find a sensitivity of global-mean precipitation to tropospheric greenhouse gas forcing of −0.42 ± 0.23%/(W/m2) (uncertainty given as one std of inter-model variability) and to black carbon emissions of −0.07 ± 0.02%/(Mt/yr). In combination with these two predictors the dominant longer-term effect of surface air temperatures on precipitation is estimated to be 2.2 ± 0.52%/K – much lower than the 6.5%/K that may be expected from the Clausius-Clapeyron relationship.” Frieler, K., M. Meinshausen, T. Schneider von Deimling, T. Andrews, and P. Forster (2011), Geophys. Res. Lett., 38, L04702, doi:10.1029/2010GL045953.

Sea level budget balanced by deep ocean heat

Deep ocean warming assessed from altimeters, Gravity Recovery and Climate Experiment, in situ measurements, and a non-Boussinesq ocean general circulation model – Song & Colberg (2011)“Observational surveys have shown significant oceanic bottom water warming, but they are too spatially and temporally sporadic to quantify the deep ocean contribution to the present-day sea level rise (SLR). In this study, altimetry sea surface height (SSH), Gravity Recovery and Climate Experiment (GRACE) ocean mass, and in situ upper ocean (0–700 m) steric height have been assessed for their seasonal variability and trend maps. It is shown that neither the global mean nor the regional trends of altimetry SLR can be explained by the upper ocean steric height plus the GRACE ocean mass. A non-Boussinesq ocean general circulation model (OGCM), allowing the sea level to rise as a direct response to the heat added into the ocean, is then used to diagnose the deep ocean steric height. Constrained by sea surface temperature data and the top of atmosphere (TOA) radiation measurements, the model reproduces the observed upper ocean heat content well. Combining the modeled deep ocean steric height with observational upper ocean data gives the full depth steric height. Adding a GRACE-estimated mass trend, the data-model combination explains not only the altimetry global mean SLR but also its regional trends fairly well. The deep ocean warming is mostly prevalent in the Atlantic and Indian oceans, and along the Antarctic Circumpolar Current, suggesting a strong relation to the oceanic circulation and dynamics. Its comparison with available bottom water measurements shows reasonably good agreement, indicating that deep ocean warming below 700 m might have contributed 1.1 mm/yr to the global mean SLR or one-third of the altimeter-observed rate of 3.11 ± 0.6 mm/yr over 1993–2008.” Song, Y. T., and F. Colberg (2011), J. Geophys. Res., 116, C02020, doi:10.1029/2010JC006601.

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Recent sea level rise has so far been difficult to fully explain: satellites measure global sea level rise since 1993 to be about 3.1 mm/year. The warming and expanding ‘upper ocean’, or the top 700 metres measured by ships and buoys can explain 1.2 mm/year whilst the water added by melting snow and ice can be estimated from satellite gravity measurements for ice sheets and other methods for smaller glaciers, and is about 0.85 mm/year.

Figure 1. Model result for sea level rise from thermal expansion of the deep ocean.

Simple addition of the numbers above (1.2 + 0.85 mm/year = 2.05 mm/year) shows that the result from the upper ocean thermal expansion and addition of water mass is still about 1 mm/year short of the observed 3.1 mm/year sea level rise. However, some previous studies have had these numbers quite close to each other when the uncertainties in the estimates have been considered.

Most of the previous studies and the analysis above are missing one thing – the effect of the deep ocean. Recent studies have shown the global deep ocean to be warming. We have also gained some knowledge of the transmission of the heat to the deep ocean, which can now occur on decadal timescales instead of previously thought centennial timescales. However, temperature measurements of the deep ocean have been very sparse, so it is difficult to estimate the thermal expansion of the deep ocean from them.

Ocean models have been an important tool for estimating sea level rise and ocean heat content, as they use physics to ‘fill in’ the data between observations. Most models conserve volume which makes thermal expansion to have no effect to the sea level, so they require so-called “Boussinesq correction” in order to estimate sea level rise from the thermal expansion of the sea water. The correction is globally uniform so the regional estimates might not be correct even if the global estimate would be good.

A new study by Song & Colberg has aimed to improve the estimates of the sea level rise. They used the sea level satellite measurements from TOPEX/Poseidon, Jason-1, ERS-1 and EVISAT. They also used gravity measurements from GRACE to determine the addition of melt-water. Thermal expansion of the upper ocean was determined from the CTD, XBT and Argo measurements. They also used a non-boussinesq ocean model to simulate the sea level budget.

The annual variability is very similar in the estimates of upper ocean thermal expansion and the measurements of the sea level rise. This suggests that the annual variability in sea level rise is originating from the thermal expansion and contraction of the upper ocean with annually varying temperatures. Also the model simulations show similar annual variability. The regional trends are remarkably different in all three data sets. This indicates that there is something missing from the sea level budget.

The model simulations generally agree with the observations rather well with some minor differences here and there. The model simulations also show the deep ocean thermal expansion. There is a long-term expanding trend. This suggests that there should be warming in the deep ocean. Model results show that especially North Atlantic and Antarctic Circumpolar Current deep waters should be warming and that the warming is related to the ocean circulation.

Figure 2. Comparison of model results and observations.

This deep ocean warming might be the reason why the sea level budget does not close. To gain a further confidence to the situation, the model results were compared to the available deep ocean measurements. The result from this comparison is a general match, even if some minor regional differences between the model results and the observations exist. The model results also show that the deep ocean warming is strongest in the Southern Ocean, which matches the results of the recent study by Purkey & Johnson.

The model simulations give a sea level rise of 1.1 mm/year from the thermal expansion of the deep ocean. When that is added to the 2.05 mm/year calculated above, the result (3.15 mm/year) is remarkably close to the observed rise of 3.1 mm/year (which more accurately is 3.11 mm/year).

Here it is important to note that most (82%) of the volume of the global ocean lies deeper than 700 meters from the surface. Therefore even slight warming in the deep ocean causes a large rise in sea level. Observations show that the upper parts of oceans have warmed for decades, which is sufficiently long time for the warming to show up in the deep ocean as well.

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Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news. Planet 3.0 also reports new research.

Published last week:

Caribbean coral reefs vanishing in simulations

Modeling regional coral reef responses to global warming and changes in ocean chemistry: Caribbean case study – Buddemeier et al. (2011)“Climatic change threatens the future of coral reefs in the Caribbean and the important ecosystem services they provide. We used a simulation model [Combo (“COral Mortality and Bleaching Output”)] to estimate future coral cover in the part of the eastern Caribbean impacted by a massive coral bleaching event in 2005. Combo calculates impacts of future climate change on coral reefs by combining impacts from long-term changes in average sea surface temperature (SST) and ocean acidification with impacts from episodic high temperature mortality (bleaching) events. We used mortality and heat dose data from the 2005 bleaching event to select historic temperature datasets, to use as a baseline for running Combo under different future climate scenarios and sets of assumptions. Results suggest a bleak future for coral reefs in the eastern Caribbean. For three different emissions scenarios from the Intergovernmental Panel on Climate Change (IPCC; B1, A1B, and A1FI), coral cover on most Caribbean reefs is projected to drop below 5% by the year 2035, if future mortality rates are equivalent to some of those observed in the 2005 event (50%). For a scenario where corals gain an additional 1–1.5°C of heat tolerance through a shift in the algae that live in the coral tissue, coral cover above 5% is prolonged until 2065. Additional impacts such as storms or anthropogenic damage could result in declines in coral cover even faster than those projected here. These results suggest the need to identify and preserve the locations that are likely to have a higher resiliency to bleaching to save as many remnant populations of corals as possible in the face of projected wide-spread coral loss.” R. W. Buddemeier, Diana R. Lane and J. A. Martinich, Climatic Change, DOI: 10.1007/s10584-011-0022-z. [full text]

Determining causes for spring advancement in North America

Northern Hemisphere Modes of Variability and the Timing of Spring in Western North America – Ault et al. (2011)“Spatial and temporal patterns of variability in spring onset are identified across western North America using a spring index (SI) model based on weather station Tmin and Tmax. Principal component analysis shows that two significant and independent patterns explain roughly half of the total variance in the timing of spring onset from 1920–2005. However, these patterns of spring onset do not appear to be linear responses to the primary modes of variability in the Northern Hemisphere: the Pacific-North American pattern (PNA) and the northern annular mode (NAM). Instead, over the period when reanalysis data and the spring index model overlap (1950–2005), the patterns of spring onset are local responses to the state of both the PNA and NAM, which together modulate the onset date of spring by 10 to 20 days on interannual timescales. They do so by controlling the number and intensity of warm days. There is also a region-wide trend in spring advancement of about −1.5 days per decade from 1950–2005. Trends in the NAM and PNA can only explain about one third (−0.5 days per decade) of this trend.” Toby R. Ault and Alison K. Macalady, Gregory T. Pederson, Julio L. Betancourt, Mark D. Schwartz, Journal of Climate 2011.

Solar irradiance at the South Pole

Solar irradiance at the earth’s surface: long-term behavior observed at the South Pole – Frederick & Hodge (2011)“This research examines a 17-year database of UV-A (320–400 nm) and visible (400–600 nm) solar irradiance obtained by a scanning spectroradiometer located at the South Pole. The goal is to define the variability in solar irradiance reaching the polar surface, with emphasis on the influence of cloudiness and on identifying systematic trends and possible links to the solar cycle. To eliminate changes associated with the varying solar elevation, the analysis focuses on data averaged over 30–35 day periods centered on each year’s austral summer solstice. The long-term average effect of South Polar clouds is a small attenuation, with the mean measured irradiances being about 5–6% less than the clear-sky values, although at any specific time clouds may reduce or enhance the signal that reaches the sensor. The instantaneous fractional attenuation or enhancement is wavelength dependent, where the percent deviation from the clear-sky irradiance at 400–600 nm is typically 2.5 times that at 320–340 nm. When averaged over the period near each year’s summer solstice, significant correlations appear between irradiances at all wavelengths and the solar cycle as measured by the 10.7 cm solar radio flux. An approximate 1.8 ± 1.0% decrease in ground-level irradiance occurs from solar maximum to solar minimum for the wavelength band 320–400 nm. The corresponding decrease for 400–600 nm is 2.4 ± 1.9%. The best-estimate declines appear too large to originate in the sun. If the correlations have a geophysical origin, they suggest a small variation in atmospheric attenuation with the solar cycle over the period of observation, with the greatest attenuation occurring at solar minimum.” Frederick, J. E. and Hodge, A. L., Atmos. Chem. Phys., 11, 1177-1189, doi:10.5194/acp-11-1177-2011, 2011. [full text]

Global analysis of anthropogenic sulfur dioxide emissions

Anthropogenic sulfur dioxide emissions: 1850–2005 – Smith et al. (2011)“Sulfur aerosols impact human health, ecosystems, agriculture, and global and regional climate. A new annual estimate of anthropogenic global and regional sulfur dioxide emissions has been constructed spanning the period 1850–2005 using a bottom-up mass balance method, calibrated to country-level inventory data. Global emissions peaked in the early 1970s and decreased until 2000, with an increase in recent years due to increased emissions in China, international shipping, and developing countries in general. An uncertainty analysis was conducted including both random and systemic uncertainties. The overall global uncertainty in sulfur dioxide emissions is relatively small, but regional uncertainties ranged up to 30%. The largest contributors to uncertainty at present are emissions from China and international shipping. Emissions were distributed on a 0.5° grid by sector for use in coordinated climate model experiments.” Smith, S. J., van Aardenne, J., Klimont, Z., Andres, R. J., Volke, A., and Delgado Arias, S., Atmos. Chem. Phys., 11, 1101-1116, doi:10.5194/acp-11-1101-2011, 2011. [full text]

Early anthropogenic effect on atmospheric CH4 and CO2

Can natural or anthropogenic explanations of late-Holocene CO2 and CH4 increases be falsified? – Ruddiman et al. (2011)“Concentrations of CO2 and CH4 in the atmosphere rose slowly during the millennia prior to the industrial era. Opposing explanations for these increases have invoked natural and anthropogenic sources. Here we revisit this argument using new evidence to see whether either explanation can be falsified (disproven, in the sense proposed by German philosopher Karl Popper). Two lines of evidence suggest that natural explanations for the CH4 increase are falsified: (1) the absence of any sustained methane increase early in seven interglaciations prior to the Holocene; and (2) weakening emissions during the last 5000 years from the two largest global sources of CH4– north tropical and boreal wetlands. Consistent with this interpretation, a new synthesis of archeological data from southern Asia reported in this issue indicates an exponential increase in CH4 emissions from expanding rice irrigation during the last 5000 years. Neither the anthropogenic nor the natural explanations for the CO2 increase can at this point be falsified. Previous studies that rejected the early anthropogenic hypothesis based on the small size of early farming populations ignored a rich array of archeological and historical evidence showing that early farmers used much more land per capita than those in the centuries just before the industrial era. Previous interpretations of very small terrestrial (anthropogenic and other) carbon emissions during the last 7000 years based on the δ13CO2 record failed to incorporate credible estimates of very large carbon burial in boreal peat lands during the late Holocene. Allowance for larger burial in peat deposits requires much greater emissions of anthropogenic carbon to balance the δ13CO2 budget. The prevalence of downward CO2 trends during equivalent intervals early in previous interglaciations poses a major problem for natural explanations of the late-Holocene CO2 increase.” W. F. Ruddiman, J. E. Kutzbach, S. J. Vavrus, The Holocene February 8, 2011, doi: 10.1177/0959683610387172.

Observations of seasonal changes in Titan

Seasonal changes in Titan’s meteorology – Turtle et al. (2011)“The Cassini Imaging Science Subsystem has observed Titan for ∼1/4 Titan year, and we report here the first evidence of seasonal shifts in preferred locations of tropospheric methane clouds. South-polar convective cloud activity, common in late southern summer, has become rare. North-polar and northern mid-latitude clouds appeared during the approach to the northern spring equinox in August 2009. Recent observations have shown extensive cloud systems at low latitudes. In contrast, southern mid-latitude and subtropical clouds have appeared sporadically throughout the mission, exhibiting little seasonality to date. These differences in behavior suggest that Titan’s clouds, and thus its general circulation, are influenced by both the rapid temperature response of a low-thermal-inertia surface and the much longer radiative timescale of Titan’s cold thick troposphere. North-polar clouds are often seen near lakes and seas, suggesting that local increases in methane concentration and/or lifting generated by surface roughness gradients may promote cloud formation.” Turtle, E. P., A. D. Del Genio, J. M. Barbara, J. E. Perry, E. L. Schaller, A. S. McEwen, R. A. West, and T. L. Ray (2011), Geophys. Res. Lett., 38, L03203, doi:10.1029/2010GL046266.

Northern Ireland temperature is controlled by water vapor, sun, and GHG’s

The role of water vapor and solar radiation in determining temperature changes and trends measured at Armagh, 1881–2000 – Stanhill (2011)“A 120 year series of climate measurements at Armagh Observatory, a rural site in Northern Ireland, was analyzed to yield monthly, seasonal, and annual values of long- and short-wave irradiances which were then related to the measured changes in air temperature. Three quarters of the significant increase and large decadal variations in atmospheric long-wave radiation was associated with the concurrent changes measured in specific humidity; the remaining quarter was associated with increases in the concentrations of carbon dioxide and other anthropogenic radiatively active gases. Significant but smaller long-term decreases in short-wave solar irradiance reduced by half the net, all-wave radiation forcing at the surface. Together the changes in long- and short-wave irradiances at Armagh accounted for more than three quarters of the interannual variations in mean annual temperatures. Climate sensitivity to long-wave forcing at the surface, 0.121°C per W m−2, was 5 times greater than that to short-wave forcing, and two possible explanations for this difference, water vapor feedback and changes in atmospheric circulation, are discussed.” Stanhill, G. (2011), J. Geophys. Res., 116, D03105, doi:10.1029/2010JD014044.

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This is a list of papers on Pacific Decadal Oscillation. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

Investigating the possibility of a human component in various pacific decadal oscillation indices – Bonfils & Santer (2010)“The pacific decadal oscillation (PDO) is a mode of natural decadal climate variability, typically defined as the principal component of North Pacific sea surface temperature (SST) anomalies. To remove any global warming signal present in the data, the traditional definition specifies that monthly-mean, global-average SST anomalies are subtracted from the local anomalies. Differences in the warming rates over the globe and the PDO region may therefore be aliased into the PDO index. Here, we examine the possibility of a human component in the PDO, considering three different definitions. The implications of these definitions are explored using SSTs from both observations and simulations of historical and future climate, all projected onto (definition-dependent) observed PDO patterns. In the twenty first century scenarios, a systematic anthropogenic component is found in all three PDO indices. Under the first definition—in which no warming signal is removed—this component is so large that it is also statistically detectable in the observed PDO. Using the second/traditional definition, this component is also large, and arises primarily from the differential warming rates predicted in the North Pacific and over global oceans. Removing the spatial average SST signal in the PDO region (in the third definition) partially solves this problem, but a human signal persists because the predicted pattern of SST response to human forcing projects strongly onto the PDO pattern. This illustrates the importance of separating internally-generated and externally-forced components in the PDO, and suggests that caution should be exercised in using PDO indices for statistical removal of “natural variability” effects from observational datasets.” Céline Bonfils and Benjamin D. Santer, Climate Dynamics, DOI: 10.1007/s00382-010-0920-1. [full text]

Pacific decadal oscillation hindcasts relevant to near-term climate prediction – Mochizuki et al. (2010)“Decadal-scale climate variations over the Pacific Ocean and its surroundings are strongly related to the so-called Pacific decadal oscillation (PDO) which is coherent with wintertime climate over North America and Asian monsoon, and have important impacts on marine ecosystems and fisheries. In a near-term climate prediction covering the period up to 2030, we require knowledge of the future state of internal variations in the climate system such as the PDO as well as the global warming signal. We perform sets of ensemble hindcast and forecast experiments using a coupled atmosphere-ocean climate model to examine the predictability of internal variations on decadal timescales, in addition to the response to external forcing due to changes in concentrations of greenhouse gases and aerosols, volcanic activity, and solar cycle variations. Our results highlight that an initialization of the upper-ocean state using historical observations is effective for successful hindcasts of the PDO and has a great impact on future predictions. Ensemble hindcasts for the 20th century demonstrate a predictive skill in the upper-ocean temperature over almost a decade, particularly around the Kuroshio-Oyashio extension (KOE) and subtropical oceanic frontal regions where the PDO signals are observed strongest. A negative tendency of the predicted PDO phase in the coming decade will enhance the rising trend in surface air-temperature (SAT) over east Asia and over the KOE region, and suppress it along the west coasts of North and South America and over the equatorial Pacific. This suppression will contribute to a slowing down of the global-mean SAT rise.” Takashi Mochizuki, Masayoshi Ishii, Masahide Kimoto, Yoshimitsu Chikamoto, Masahiro Watanabe, Toru Nozawa, Takashi T. Sakamoto, Hideo Shiogama, Toshiyuki Awaji, Nozomi Sugiura, Takahiro Toyoda, Sayaka Yasunaka, Hiroaki Tatebe, and Masato Mori, PNAS February 2, 2010 vol. 107 no. 5 1833-1837, doi: 10.1073/pnas.0906531107. [full text]

The Role of Tropospheric Rossby Wave Breaking in the Pacific Decadal Oscillation – Strong & Magnusdottir (2009)“The leading pattern of extratropical Pacific sea surface temperature variability [the Pacific decadal oscillation (PDO)] is shown to depend on observed variability in the spatiotemporal distribution of tropospheric Rossby wave breaking (RWB), where RWB is the irreversible overturning of potential vorticity on isentropic surfaces. Composite analyses based on hundreds of RWB cases show that anticyclonic (cyclonic) RWB is associated with a warm, moist (cool, dry) column that extends down to a surface anticyclonic (cyclonic) circulation, and that the moisture and temperature advection associated with the surface circulation patterns force turbulent heat flux anomalies that project onto the spatial pattern of the PDO. The RWB patterns that are relevant to the PDO are closely tied to El Niño–Southern Oscillation, the Pacific–North American pattern, and the northern annular mode. These results explain the free troposphere-to-surface segment of the atmospheric bridge concept wherein El Niño anomalies emerge in summer and modify circulation patterns that act over several months to force sea surface temperature anomalies in the extratropical Pacific during late winter or early spring. Leading patterns of RWB account for a significant fraction of PDO interannual variability for any month of the year. A multilinear model is developed in which the January mean PDO index for 1958–2006 is regressed upon the leading principal components of cyclonic and anticyclonic RWB from the immediately preceding winter and summer months (four indexes in all), accounting for more than two-thirds of the variance.” Strong, Courtenay, Gudrun Magnusdottir, 2009: J. Climate, 22, 1819–1833.

Tropical origins of North and South Pacific decadal variability – Shakun & Shaman (2009)“The origin of the Pacific Decadal Oscillation (PDO), the leading mode of sea surface temperature variability for the North Pacific, is a matter of considerable debate. One paradigm views the PDO as an independent mode centered in the North Pacific, while another regards it as a largely reddened response to El Niño-Southern Oscillation (ENSO) forcing from the tropics. We calculate the Southern Hemisphere equivalent of the PDO index based on the leading mode of sea surface temperature variability for the South Pacific and find that it adequately explains the spatial structure of the PDO in the North Pacific. A first-order autoregressive model forced by ENSO is used to reproduce the observed PDO indices in the North and South Pacific. These results highlight the strong similarity in Pacific decadal variability on either side of the equator and suggest it may best be viewed as a reddened response to ENSO.” Shakun, J. D., and J. Shaman (2009), Geophys. Res. Lett., 36, L19711, doi:10.1029/2009GL040313. [full text]

The 18.6-year period moon-tidal cycle in Pacific Decadal Oscillation reconstructed from tree-rings in western North America – Yasuda (2009)“Time-series of Pacific Decadal Oscillation (PDO) reconstructed from tree-rings in Western North America is found to have a statistically significant periodicity of 18.6-year period lunar nodal tidal cycle; negative (positive) PDO tends to occur in the period of strong (weak) diurnal tide. In the 3rd and 5th (10th, 11th and 13rd) year after the maximum diurnal tide, mean-PDO takes significant negative (positive) value, suggesting that the Aleutian Low is weak (strong), western-central North Pacific in 30–50°N is warm (cool) and equator-eastern rim of the Pacific is cool (warm). This contributes to climate predictability with a time-table from the astronomical tidal cycle.” Yasuda, I. (2009), Geophys. Res. Lett., 36, L05605, doi:10.1029/2008GL036880.

On the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation: Might they be related? – d’Orgeville & Peltier (2007)“The nature of the Pacific Decadal Oscillation (PDO) is investigated based upon analyses of sea surface temperature observations over the last century. The PDO is suggested to be comprised of a 20 year quasi-periodic oscillation and a lower frequency component with a characteristic timescale of 60 years. The 20 year quasi-periodic oscillation is clearly identified as a phase locked signal at the eastern boundary of the Pacific basin, which could be interpreted as the signature of an ocean basin mode. We demonstrate that the 60 year component of the PDO is strongly time-lag correlated with the Atlantic Multidecadal Oscillation (AMO). On this timescale the AMO is shown to lead the PDO by approximately 13 years or to lag the PDO by 17 years. This relation suggests that the AMO and the 60 year component of the PDO are signatures of the same oscillation cycle” d’Orgeville, M., and W. R. Peltier (2007), Geophys. Res. Lett., 34, L23705, doi:10.1029/2007GL031584.

Secular variation of the Pacific Decadal Oscillation, the North Pacific Oscillation and climatic jumps in a multi-millennial simulation – Hunt (2007)“Outputs from a 10,000-year simulation with a coupled global climatic model for present climatic conditions have been used to investigate the behaviour of the Pacific Decadal Oscillation (PDO), the North Pacific Oscillation (NPO) and related phenomena. The analysis reveals a wide range of temporal variability for these Oscillations, suggesting that observations to date provide only a limited sample of possible outcomes. In addition, the simulation suggests that the current observed phase relation between the PDO and NPO may not be typical of longer-term variability. Climatic jumps appear to be a ubiquitous feature of climatic variability, and while, as observed, the most common interval between such jumps is about 20 years, intervals of up to 100 years occur in the simulation. The probability density functions of the PDO and NPO are very close to Gaussian, with the PDO being represented by an auto-regressive function of order one, while the NPO consisted of white noise. An FFT analysis of PC1 of the PDO revealed periodicities concentrated near 10 years, while for the NPO the principal periodicities were decadal to bidecadal. Global distributions of the distributions of the correlations between PC1 or the NPO and selected climatic variables were similar, and in agreement with observations. These correlations highlight the inter-relationships between these two Oscillations. The above correlations were not necessarily stable in time for a given geographical point, with transitions occurring between positive and negative extremes. Climatic jumps were identified with transitions of both the PDO and NPO, with magnitudes of importance as regards climatic perturbations. Spatial patterns of the changes associated with such jumps have global scales, and the need to consider the implications of these jumps in regard to greenhouse induced climatic change is noted.” B. G. Hunt, Climate Dynamics, Volume 30, Number 5, 467-483, DOI: 10.1007/s00382-007-0307-0.

A Pacific Decadal Oscillation record since 1470 AD reconstructed from proxy data of summer rainfall over eastern China – Shen et al. (2006)“Recent studies indicated that the spatial pattern and temporal variability of summer rainfall over eastern China are well correlated with the Pacific Decadal Oscillation (PDO). Here we used a data set of the drought/flood index (a proxy of summer rainfall) since 1470 AD to reconstruct the annual PDO index. The reconstruction indicates that the PDO is a robust feature of North Pacific climate variability throughout the study period, however, the major modes of oscillation providing the basic PDO regime timescale have not been persistent over the last 530 years. The quasi-centennial (75–115-yr) and pentadecadal (50–70-yr) oscillations dominated the periods before and after 1850, respectively. Our analysis suggest that solar forcing fluctuation on quasi-centennial time scale (Gleissberg cycle) could be the pace-maker of the PDO before 1850, and the PDO behavior after 1850 could be due, in part, to the global warming.” Shen, C., W.-C. Wang, W. Gong, and Z. Hao (2006), Geophys. Res. Lett., 33, L03702, doi:10.1029/2005GL024804.

Variations in the Pacific Decadal Oscillation over the past millennium – MacDonald & Case (2005)“Hydrologically sensitive tree-ring chronologies from Pinus flexilis in California and Alberta were used to produce an AD 993–1996 reconstruction of the Pacific Decadal Oscillation (PDO) and to assess long-term variability in the PDO’s strength and periodicity. The reconstruction indicates that a ∼50 to 70 year periodicity in the PDO is typical for the past 200 years but, was only intermittently a strong mode of variability prior to that. Between AD 1600 and 1800 there is a general absence of significant variability within the 50 to 100 year frequency range. Significant variability within in the frequency range of 50 to 100 years reemerges between AD 1500 and 1300 and AD 1200 to 1000. A prolonged period of strongly negative PDO values between AD 993 and 1300 is contemporaneous with a severe medieval megadrought that is apparent in many proxy hydrologic records for the western United States and Canada.” MacDonald, G. M., and R. A. Case (2005), Geophys. Res. Lett., 32, L08703, doi:10.1029/2005GL022478. [full text]

The Forcing of the Pacific Decadal Oscillation – Schneider & Cornuelle (2005)“The Pacific decadal oscillation (PDO), defined as the leading empirical orthogonal function of North Pacific sea surface temperature anomalies, is a widely used index for decadal variability. It is shown that the PDO can be recovered from a reconstruction of North Pacific sea surface temperature anomalies based on a first-order autoregressive model and forcing by variability of the Aleutian low, El Niño–Southern Oscillation (ENSO), and oceanic zonal advection anomalies in the Kuroshio–Oyashio Extension. The latter results from oceanic Rossby waves that are forced by North Pacific Ekman pumping. The SST response patterns to these processes are not orthogonal, and they determine the spatial characteristics of the PDO. The importance of the different forcing processes is frequency dependent. At interannual time scales, forcing from ENSO and the Aleutian low determines the response in equal parts. At decadal time scales, zonal advection in the Kuroshio–Oyashio Extension, ENSO, and anomalies of the Aleutian low each account for similar amounts of the PDO variance. These results support the hypothesis that the PDO is not a dynamical mode, but arises from the superposition of sea surface temperature fluctuations with different dynamical origins.” Schneider, Niklas, Bruce D. Cornuelle, 2005, J. Climate, 18, 4355–4373. [full text]

ENSO-Forced Variability of the Pacific Decadal Oscillation – Newman et al. (2003)“Variability of the Pacific decadal oscillation (PDO), on both interannual and decadal timescales, is well modeled as the sum of direct forcing by El Niño–Southern Oscillation (ENSO), the “reemergence” of North Pacific sea surface temperature anomalies in subsequent winters, and white noise atmospheric forcing. This simple model may be taken as a null hypothesis for the PDO, and may also be relevant for other climate integrators that have been previously related to the PDO.” Newman, Matthew, Gilbert P. Compo, Michael A. Alexander, 2003, J. Climate, 16, 3853–3857. [full text]

The Pacific Decadal Oscillation – Mantua & Hare (2002)“The Pacific Decadal Oscillation (PDO) has been described by some as a long-lived El Niño-like pattern of Pacific climate variability, and by others as a blend of two sometimes independent modes having distinct spatial and temporal characteristics of North Pacific sea surface temperature (SST) variability. A growing body of evidence highlights a strong tendency for PDO impacts in the Southern Hemisphere, with important surface climate anomalies over the mid-latitude South Pacific Ocean, Australia and South America. Several independent studies find evidence for just two full PDO cycles in the past century: “cool” PDO regimes prevailed from 1890–1924 and again from 1947–1976, while “warm” PDO regimes dominated from 1925–1946 and from 1977 through (at least) the mid-1990’s. Interdecadal changes in Pacific climate have widespread impacts on natural systems, including water resources in the Americas and many marine fisheries in the North Pacific. Tree-ring and Pacific coral based climate reconstructions suggest that PDO variations—at a range of varying time scales—can be traced back to at least 1600, although there are important differences between different proxy reconstructions. While 20th Century PDO fluctuations were most energetic in two general periodicities—one from 15-to-25 years, and the other from 50-to-70 years—the mechanisms causing PDO variability remain unclear. To date, there is little in the way of observational evidence to support a mid-latitude coupled air-sea interaction for PDO, though there are several well-understood mechanisms that promote multi-year persistence in North Pacific upper ocean temperature anomalies.” Nathan J. Mantua and Steven R. Hare, Journal of Oceanography, Volume 58, Number 1, 35-44, DOI: 10.1023/A:1015820616384.

A Pacific Interdecadal Climate Oscillation with Impacts on Salmon Production – Mantua et al. (1997)“Evidence gleaned from the instrumental record of climate data identifies a robust, recurring pattern of ocean–atmosphere climate variability centered over the midlatitude North Pacific basin. Over the past century, the amplitude of this climate pattern has varied irregularly at interannual-to-interdecadal timescales. There is evidence of reversals in the prevailing polarity of the oscillation occurring around 1925, 1947, and 1977; the last two reversals correspond to dramatic shifts in salmon production regimes in the North Pacific Ocean. This climate pattern also affects coastal sea and continental surface air temperatures, as well as streamflow in major west coast river systems, from Alaska to California.” Mantua, Nathan J., Steven R. Hare, Yuan Zhang, John M. Wallace, Robert C. Francis, 1997, Bull. Amer. Meteor. Soc., 78, 1069–1079. [full text]

ENSO-like Interdecadal Variability: 1900–93 – Zhang et al. (1997)“A number of recent studies have reported an ENSO-like EOF mode in the global sea surface temperature (SST) field, whose time variability is marked by an abrupt change toward a warmer tropical eastern Pacific and a colder extratropical central North Pacific in 1976–77. The present study compares this pattern with the structure of the interannual variability associated with the ENSO cycle and documents its time history back to 1900. The analysis is primarily based on the leading EOFs of the SST anomaly and “anomaly deviation” fields in various domains and the associated expansion coefficient (or principal component) time series, which are used to construct global regression maps of SST, sea level pressure (SLP), and a number of related variables. The use of “anomaly deviations” (i.e., departures of local SST anomalies from the concurrent global-mean SST anomaly) reduces the influence of global-mean SST trends upon the structure of the EOFs and their expansion coefficient time series. An important auxiliary time series used in this study is a “Southern Oscillation index” based on marine surface observations. By means of several different analysis techniques, the time variability of the leading EOF of the global SST field is separated into two components: one identified with the “ENSO cycle-related” variability on the interannual timescale, and the other a linearly independent “residual” comprising all the interdecadal variability in the record. The two components exhibit rather similar spatial signatures in the global SST, SLP, and wind stress fields. The SST signature in the residual variability is less equatorially confined in the eastern Pacific and it is relatively more prominent over the extratropical North Pacific. The corresponding SLP signature is also stronger over the extratropical North Pacific, and its counterpart in the cold season 500-mb height field more closely resembles the PNA pattern. The amplitude time series of the ENSO-like pattern in the residual variability reflects the above-mentioned shift in 1976–77, as well as a number of other prominent features, including a shift of opposite polarity during the 1940s.” Zhang, Yuan, John M. Wallace, David S. Battisti, 1997: ENSO-like Interdecadal Variability: 1900–93. J. Climate, 10, 1004–1020. [full text]

Decadal Climate Variability over the North Pacific and North America: Dynamics and Predictability – Latif & Barnett (1995)“The dynamics and predictability of decadal climate variability over the North Pacific and North America are investigated by analyzing various observational datasets and the output of a state of the art coupled ocean–atmosphere general circulation model that was integrated for 125 years. Both the observations and model results support the picture that the decadal variability in the region of interest is based on a cycle involving unstable ocean–atmosphere interactions over the North Pacific. The period of this cycle is of the order of a few decades. The cycle involves the two major circulation regimes in the North Pacific climate system, the subtropical ocean gyre, and the Aleutian low. When, for instance, the subtropical ocean gyre is anomalously strong, more warm tropical waters are transported poleward by the Kuroshio and its extension, leading to a positive SST anomaly in the North Pacific. The atmospheric response to this SST anomaly involves a weakened Aleutian low, and the associated fluxes at the air–sea interface reinforce the initial SST anomaly, so that ocean and atmosphere act as a positive feedback system. The anomalous heat flux, reduced ocean mixing in response to a weakened storm track, and anonmalous Ekman heat transport contribute to this positive feedback. The atmospheric response, however, consists also of a wind stress curl anomaly that spins down the subtropical ocean gyre, thereby reducing the poleward heat transport and the initial SST anomaly. The ocean adjusts with some time lag to the change in the wind stress curl, and it is this transient ocean response that allows continuous oscillations. The transient response can be expressed in terms of baroclinic planetary waves, and the decadal timescale of the oscillation is therefore determined to first order by wave timescales. Advection by the mean currents, however, is not negligible. The existence of such a cycle provides the basis of long-range climate forecasting over North America at decadal timescales. At a minimum, knowledge of the present phase of the decadal mode should allow a “now-cast” of expected climate “bias” over North America, which is equivalent to a climate forecast several years ahead.” Latif, M., T. P. Barnett, 1996, J. Climate, 9, 2407–2423.. [full text]

A century and a half of change in the climate of the NE Pacific – Ware (1995)“Spectral analysis of twenty-one climate records indicates that NE Pacific temperatures and winter wind stress have fluctuated at four dominant time scales in this century: 2–3 years (quasi-biennial oscillation), 5–7 years (El Nin̈o-Southern Oscillation, ENSO), 20–25 years (bidecadal oscillation, BDO), and a poorly resolved, very-low-frequency (VLF) oscillation with a 50–75 year period. Forty-four per cent of the low-frequency variability in British Columbia air temperatures is associated with the strength of the Aleutian Low pressure system in winter. Only 42% of the ‘strong’ and 25% of the ‘moderate’ ENSO events in this century have produced large warm anomalies off BC. Interactions between the ENSO, bidecadal and very-low-frequency oscillations produce a pattern of alternating warm and cool climate states, with major warnings every 50 to 75 years. Since 1850 there have been seven warm periods, lasting an average of 11.4 years, and six cool periods lasting an average of 10.8 years. Sharp transitions from cool to warm climate states (as in 1977/78) occur when warming phases of the BDO and VLF oscillations coincide. Recent evidence suggests that the BDO may originate in either the tropical or the subtropical North Pacific. The NE Pacific has experienced a major warming since 1978. A long-range forecast suggests that the BDO and VLF oscillations peaked in 1989 and are currently in a cooling phase. Consequently, coastal temperatures should moderate for the rest of this century. A transition to the next cool climate state could occur about the year 2001. The forecast for moderating temperatures could begin the first phase of the recovery of the southern BC coastal chinook and coho salmon and herring stocks, which are currently at low abundance levels.” D.M. Ware, Fisheries Oceanography, Volume 4, Issue 4, pages 267–277, December 1995.

Causes of Decadal Climate Variability over the North Pacific and North America – Latif & Barnett (1994)“The cause of decadal climate variability over the North Pacific Ocean and North America is investigated by the analysis of data from a multidecadal integration with a state-of-the-art coupled ocean-atmosphere model and observations. About one-third of the low-frequency climate variability in the region of interest can be attributed to a cycle involving unstable air-sea interactions between the subtropical gyre circulation in the North Pacific and the Aleutian low-pressure system. The existence of this cycle provides a basis for long-range climate forecasting over the western United States at decadal time scales.” M. Latif and T. P. Barnett, Science 28 October 1994, Vol. 266 no. 5185 pp. 634-637, DOI: 10.1126/science.266.5185.634. [full text]

Decadal-scale regime shifts in the large marine ecosystems of the North-east Pacific: a case for historical science – Francis & Hare (1994)“There are two fundamental ways of doing science: the experimental-predictive and the historical-descriptive. The experimental-predictive approach uses the techniques of controlled experiment, the reduction of natural complexity to a minimal set of general causes, and presupposes that all times can be treated alike and adequately simulated in the laboratory. The historical-descriptive approach uses a mode of analysis which is rooted in the comparative and observational richness of our data, is holistic in its treatment of systems and events, and assumes that the final result being studied is unique, i.e. dependent or contingent upon everything that came before. We suggest that one of the real difficulties we have in understanding ecosystem properties is our inability to deal with scale, and we show how historical science allows us to approach the issue of scale through the interpretation of pattern in time and space. We then use the techniques of the historical-descriptive approach to doing science in the context of our own and other research on climate change and biological production in the North-east Pacific Ocean. In particular, we examine rapid decadal-scale shifts in the abundance and distribution of two major components–salmon and zooplankton – of the large marine ecosystem of the North-east Pacific, and how they relate to similar shifts in North Pacific atmosphere and ocean climate. We conclude that they are all related, and that climate-driven regime shifts, such as those we have identified in the North-east Pacific, can cause major reorganizations of ecological relationships over vast oceanic regions.” Robert C. Francis, Steven R. Hare, Fisheries Oceanography, Volume 3, Issue 4, pages 279–291, December 1994. [full text]

Linkage of ocean and fjord dynamics at decadal period – Ebbesmeyer et al. (1989)“At decadal period (10­20 years), dynamic linkage was evident between atmospheric low pressure systems over the North Pacific Ocean and circulation in a Pacific Northwest fjord (Puget Sound). As the Aleutian low pressure center shifts, storms arriving from the North Pacific Ocean deposit varying amounts of precipitation in the mountains draining into the estuarine system; in turn, the fluctuating addition of fresh water changes the density distribution near the fjord basin entrance sill, thereby constraining the fjord’s vertical velocity structure. The linkage was examined using time series of 21 environmental parameters which covaried between the 2 regimes associated with cycling of the Aleutian Low between its eastern and westernmost winter positions. Observations from 1899 to 1987 suggest that, in the 20th century, approximately 5 cycles may have occurred between these regimes. Covariation in all but one of the time series (Puget Sound’s main basin salinity) occurred because of the high degree of correlation between parameters and the strong decadal cycles compared with long-term averages, interannual variability, and seasonal cycles. Basin salinity was relatively steady due to opposing influences of oceanic source water salinity and the addition of fresh water in each regime. However, the decadal signal for the other parameters characterizing Puget Sound water are apparently amplified twofold compared with that of the atmosphere over the North Pacific Ocean.” Ebbesmeyer, C.C., C.A. Coomes, G.A. Cannon, and D.E. Bretschneider, In Aspects of Climate Variability in the Pacific and the Western Americas, D.J. Peterson (ed.), Geophys. Monogr. 55, American Geophysical Union, Wash., D.C., 399–417 (1989).

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Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news. Planet 3.0 also reports new research.

Published last week:

Possibly no vegetation in Antarctic peninsula during pliocene interglacials

How likely was a green Antarctic Peninsula during warm Pliocene interglacials? A critical reassessment based on new palynofloras from James Ross Island – Salzmann et al. (2011)“The question of whether Pliocene climate was warm enough to support a substantial vegetation cover on Antarctica is of great significance to the ongoing and controversial debate on the stability or dynamism of Antarctic ice sheets during warm periods with high atmospheric greenhouse gas concentrations. Here we present a systematic palynological comparison of pollen and dinoflagellate cyst assemblages from Early Pliocene diamictites and underlying late Cretaceous sediments collected from James Ross Island, northern Antarctic Peninsula. The diamictites are dated using a combination of 40Ar/39Ar and 87Sr/86Sr isotope ages on interbedded lavas and pristine bivalves. Well preserved pectinid shells and cheilostome bryozoans suggest that the palynomorph-bearing sediments were probably deposited during warmer Pliocene interglacials and later amalgamated into a diamtictite formed by a major ice advance during cold glacial cycle. The palynological analyses presented herein do not identify any in-situ pollen and spores which indicate the presence of a substantial vegetation cover. Our study suggests a local (i.e. James Ross Island) provenance for most of the diamictites, whilst sediments from the western coast might have been delivered by ice sheets from the Antarctic Peninsula. Whilst the acritarch Leiosphaeridia might imply the presence of sea-ice and near-modern climate conditions during the Late Neogene, the presence of the dinoflagellate cyst Bitectatodinium tepikiense at one location suggests that sea surface temperatures might have been substantially warmer during some interglacials. The absence of in-situ pollen and spores in the James Ross Island diamictites cannot be taken as proof of non-existence of vegetation. However, the combined palynological and geological evidence presented in this paper makes the presence of a substantial Pliocene vegetation cover on James Ross Island unlikely and supports previous reconstructions of a permanent ice sheet on the Antarctic Peninsula throughout the Late Neogene.” Ulrich Salzmann, James B. Riding, Anna E. Nelson, and John L. Smellie, Palaeogeography, Palaeoclimatology, Palaeoecology, doi:10.1016/j.palaeo.2011.01.028.

Age of blue-ice moraines suggests that WAIS survived last interglacial

Do blue-ice moraines in the Heritage Range show the West Antarctic ice sheet survived the last interglacial? – Fogwill et al. (2011)“We present a hypothesis that best explains cosmogenic isotope data on blue-ice moraines in the Heritage Range, West Antarctica. The age of the moraines implies that they, and the related ice-sheet surface with which they are associated, have persisted on the flanks of nunataks throughout at least the last interglacial/glacial cycle. The implication is that although the West Antarctic Ice Sheet (WAIS) may have fluctuated in thickness during glacial cycles, the central dome has remained intact for at least 200 kyr and possibly even for 400 kyr. Such a finding, if substantiated, would contribute to our understanding of the sensitivity of the WAIS to climate change. Further it would be a powerful geomorphic constraint on models of the past behaviour of the ice sheet during glacial cycles and thus those predicting the future of the ice sheet in a warming world.” Christopher J. Fogwill, Andrew S. Hein, Michael J. Bentley, and David E. Sugden, Palaeogeography, Palaeoclimatology, Palaeoecology, doi:10.1016/j.palaeo.2011.01.027.

Review of mountain water resources

Climate change and mountain water resources: overview and recommendations for research, management and policy – Viviroli et al. (2011)“Mountains are essential sources of freshwater for our world, but their role in global water resources could well be significantly altered by climate change. How well do we understand these potential changes today, and what are implications for water resources management, climate change adaptation, and evolving water policy? To answer above questions, we have examined 11 case study regions with the goal of providing a global overview, identifying research gaps and formulating recommendations for research, management and policy. After setting the scene regarding water stress, water management capacity and scientific capacity in our case study regions, we examine the state of knowledge in water resources from a highland-lowland viewpoint, focusing on mountain areas on the one hand and the adjacent lowland areas on the other hand. Based on this review, research priorities are identified, including precipitation, snow water equivalent, soil parameters, evapotranspiration and sublimation, groundwater as well as enhanced warming and feedback mechanisms. In addition, the importance of environmental monitoring at high altitudes is highlighted. We then make recommendations how advancements in the management of mountain water resources under climate change could be achieved in the fields of research, water resources management and policy as well as through better interaction between these fields. We conclude that effective management of mountain water resources urgently requires more detailed regional studies and more reliable scenario projections, and that research on mountain water resources must become more integrative by linking relevant disciplines. In addition, the knowledge exchange between managers and researchers must be improved and oriented towards long-term continuous interaction.” Viviroli, D., Archer, D. R., Buytaert, W., Fowler, H. J., Greenwood, G. B., Hamlet, A. F., Huang, Y., Koboltschnig, G., Litaor, M. I., López-Moreno, J. I., Lorentz, S., Schädler, B., Schreier, H., Schwaiger, K., Vuille, M., and Woods, R., Hydrol. Earth Syst. Sci., 15, 471-504, doi:10.5194/hess-15-471-2011, 2011. [full text]

Temperature extremes change in observations and climate model

Global changes in indices describing moderate temperature extremes from the daily output of a climate model – Russo & Sterl (2011)“Climate change indices derived from daily climate model temperature output are computed and analyzed to study the change of moderate climatic extremes between 1950 and 2100. We used output from the Ensemble Simulations of Extreme Weather Events Under Nonlinear Climate Change (ESSENCE) project, in which a 17-member ensemble simulation of climate change in response to the SRES A1b scenario has been carried out using the ECHAM5/MPI-OM climate model developed at the Max-Planck-Institute for Meteorology in Hamburg. The large size of the data set gives the opportunity to accurately detect the change of extreme climate indicators. We choose indices describing moderately extreme temperatures from the Expert Team on Climate Change Detection, Monitoring and Indices, focusing on percentile-based and duration indices. Additionally, we define some new indices measuring the intensity of daily temperature extremes. To study extremes within different consecutive 50 year time intervals (1950–2000, 2001–2050, and 2051–2100), we use corresponding reference periods (1961–1990, 2011–2040, and 2061–2090, respectively). Trends of the indices within each of the three 50-year periods are estimated using the Mann-Kendall slope estimator. The trends found in our model output for the period 1950–2000 compare well with those reported in the literature from observations. Future trend patterns resemble those from the 1950–2000 period, but have larger amplitudes. This suggests that the pattern of extreme temperature change might already emerge from the weather noise. Outside the tropics, the trend of indices defined from minimum daily temperatures is greater in absolute value than the trend of indicators related to maximum daily temperatures. The trend of the annual temperature range (Tmax − Tmin) is positive or close to zero over the tropics and negative over the extratropics, indicating that the value of the yearly maximum temperature is increasing faster than the minimum temperature in the tropics and vice versa in the extratropics. Finally, using the empirical distribution, we study the probability distribution functions (PDFs) of the occurrence of cold nights and warm days for nine regions. All PDFs shift in the direction of warming.” Russo, S., and A. Sterl (2011), J. Geophys. Res., 116, D03104, doi:10.1029/2010JD014727.

Stratospheric cooling distracts ozone measurements

Quantifying stratospheric ozone trends: Complications due to stratospheric cooling – McLinden & Fioletov (2011)“Recent studies suggest that ozone turnaround (the second stage of ozone recovery) is near. Determining precisely when this occurs, however, will be complicated by greenhouse gas-induced stratospheric cooling as ozone trends derived from profile data in different units and/or vertical co-ordinates will not agree. Stratospheric cooling leads to simultaneous trends in air density and layer thicknesses, confounding the interpretation of ozone trends. A simple model suggests that instruments measuring ozone in different units may differ as to the onset of turnaround by a decade, with some indicting a continued decline while others an increase. This concept was illustrated by examining the long-term (1979–2005) ozone trends in the SAGE (Stratospheric Aerosol and Gas Experiment) and SBUV (Solar Backscatter Ultraviolet) time series. Trends from SAGE, which measures number density as a function of altitude, and SBUV, which measures partial column as a function of pressure, are known to differ by 4–6%/decade in the upper stratosphere. It is shown that this long-standing difference can be reconciled to within 2%/decade when the trend in temperature is properly accounted for.” McLinden, C. A., and V. Fioletov (2011), Geophys. Res. Lett., 38, L03808, doi:10.1029/2010GL046012.

No evidence of cyclicity of D-O events

Characterizing the statistical properties and interhemispheric distribution of Dansgaard-Oeschger events – Thomas et al. (2011)“Ice core records from Greenland show times of rapid warming, called Dansgaard-Oeschger events, during the most recent glacial period. Characterizing the nature of Dansgaard-Oeschger events is critical to our understanding of past glacial climates, as well as modern climate volatility. Here we present new methods for statistically evaluating two important characteristics of these rapid warming events which have been highly debated in the scientific community: whether their occurrence is cyclical and whether they have a regional or global distribution. We find that there is not enough evidence to conclude that Dansgaard-Oeschger events are cyclical; yet, importantly, there is a statistically significant lagged correlation between the Antarctica and Greenland records. These results may suggest that rapid warming events in Greenland are driven by internal climate variability and strongly imply that rapid climate changes in Greenland are led by smaller amplitude changes in Antarctica through an oceanic teleconnection.” Thomas, A. M., S. Rupper, and W. F. Christensen (2011), J. Geophys. Res., 116, D03103, doi:10.1029/2010JD014834.

Ship aerosol plumes cause changes in clouds

Microphysical and macrophysical responses of marine stratocumulus polluted by underlying ships: Evidence of cloud deepening – Christensen & Stephens (2011)“Ship tracks observed by the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) were analyzed to determine the extent to which aerosol plumes from ships passing below marine stratocumulus alter the microphysical and macrophysical properties of the clouds. Moderate Resolution Imaging Spectroradiometer (MODIS) imagery was used to distinguish ship tracks embedded in closed, open, and undefined mesoscale cellular cloud structures. The impact of aerosol on the microphysical cloud properties in both the closed and open cell regimes were consistent with the changes predicted by the Twomey hypothesis. For the macrophysical changes, differences were observed between regimes. In the open cell regime, polluted clouds had significantly higher cloud tops (16%) and more liquid water (39%) than nearby unpolluted clouds. However, in the closed cell regime, polluted clouds exhibited no change in cloud top height and had less liquid water (−6%). Both microphysical (effective radius) and macrophysical (liquid water path) cloud properties contribute to a fractional change in cloud optical depth; in the closed cell regime the microphysical contribution was 3 times larger than the macrophysical contribution. However, the opposite was true in the open cell regime where the macrophysical contribution was nearly 2 times larger than the microphysical contribution because the aerosol probably increased cloud coverage. The results presented here demonstrate key differences aerosols have on the microphysical and macrophysical responses of boundary layer clouds between mesoscale stratocumulus convective regimes.” Christensen, M. W., and G. L. Stephens (2011), J. Geophys. Res., 116, D03201, doi:10.1029/2010JD014638.

Snow melts earlier in Eurasian Arctic

Change in spring snowmelt timing in Eurasian Arctic rivers – Tan et al. (2011)“Changes in the amount and timing of the discharge of major Eurasian Arctic rivers have been well documented, but whether or not these changes can be attributed to climatic factors or to the construction of manmade reservoirs remains unclear. Here we endeavor to identify the key processes (snow cover and air temperature) that have regulated seasonal streamflow fluctuations in the Eurasian Arctic over the last half-century (1958–1999) and to understand the regional coherence of timing trends, using a set of Eurasian Arctic rivers selected specifically because they are free of known effects of dams. We find a shift toward earlier onset of spring runoff as measured by a modest change in the spring pulse onset (26 of 45 stations) and a strong change in the centroid of timing (39 of 45 stations). Winter streamflows increased over the period of record in most rivers, suggesting that trends observed by others in larger regulated Eurasian Arctic rivers may not be entirely attributable to reservoir construction. Upward trends in air temperature appeared to have had the largest impact on spring and summer flows for tributaries in the coldest of the major Eurasian Arctic river basins (e.g., the Lena). While the overall duration of snow cover has not significantly changed across the Eurasian Arctic, snow cover disappearance has trended earlier in the year and appears to be related to the increased May and snowmelt season fractional flows.” Tan, A., J. C. Adam, and D. P. Lettenmaier (2011), J. Geophys. Res., 116, D03101, doi:10.1029/2010JD014337.

Warming Atlantic cools the Pacific

Tropical Pacific response to 20th century Atlantic warming – Kucharski et al. (2011)“The analysis of a series of regionally coupled ocean-atmospheric simulations suggests that the Atlantic warming that has occurred in the 20th century may have reduced the concomitant warming in the eastern tropical Pacific. The Pacific response to the Atlantic warming shows La Nina-like features even in the presence of greenhouse gas (GHG) forcing. The physical mechanism for the Atlantic warming influence on the tropical Pacific is a change in the Walker circulation that results in easterly surface wind anomalies in the central-west Pacific. Coupled ocean-atmosphere processes then amplify the signal. The possibility of an Atlantic Ocean induced cooling of the eastern tropical Pacific is complementary to the hypothesis that the GHG forcing itself may have caused the observed relative eastern Pacific cooling. It is argued that the uncertainties in the projected future mean state in the Pacific may be partly due to the competition of the GHG induced warming and the Atlantic induced cooling.” Kucharski, F., I.-S. Kang, R. Farneti, and L. Feudale (2011), Geophys. Res. Lett., 38, L03702, doi:10.1029/2010GL046248.

More nanodiamond evidence for impact hypothesis of YD event

Discovery of a nanodiamond-rich layer in the Greenland ice sheet – Kurbatov et al. (2011)“We report the discovery in the Greenland ice sheet of a discrete layer of free nanodiamonds (NDs) in very high abundances, implying most likely either an unprecedented influx of extraterrestrial (ET) material or a cosmic impact event that occurred after the last glacial episode. From that layer, we extracted n-diamonds and hexagonal diamonds (lonsdaleite), an accepted ET impact indicator, at abundances of up to about 5×106 times background levels in adjacent younger and older ice. The NDs in the concentrated layer are rounded, suggesting they most likely formed during a cosmic impact through some process similar to carbon-vapor deposition or high-explosive detonation. This morphology has not been reported previously in cosmic material, but has been observed in terrestrial impact material. This is the first highly enriched, discrete layer of NDs observed in glacial ice anywhere, and its presence indicates that ice caps are important archives of ET events of varying magnitudes. Using a preliminary ice chronology based on oxygen isotopes and dust stratigraphy, the ND-rich layer appears to be coeval with ND abundance peaks reported at numerous North American sites in a sedimentary layer, the Younger Dryas boundary layer (YDB), dating to 12.9±0.1 ka. However, more investigation is needed to confirm this association.” Kurbatov, Andrei V.; Mayewski, Paul A.; Steffensen, Jorgen P.; West, Allen; Kennett, Douglas J.; Kennett, James P.; Bunch, Ted E.; Handley, Mike; Introne, Douglas S.; Que Hee, Shane S.; Mercer, Christopher; Sellers, Marilee; Shen, Feng; Sneed, Sharon B.; Weaver, James C.; Wittke, James H.; Stafford, Thomas W.; Donovan, John J.; Xie, Sujing; Razink, Joshua J.; Stich, Adrienne; Kinzie, Charles R.; Wolbach, Wendy S., Journal of Glaciology, Volume 56, Number 199, December 2010 , pp. 747-757(11), DOI: 10.3189/002214310794457191. [full text]

Here are some papers written by Willi Dansgaard. The emphasis is on the papers that have full text freely available:

Validity of the temperature reconstruction from water isotopes in ice cores – Jouzel & Dansgaard et al. (1997)“Well-documented present-day distributions of stable water isotopes (HDO and H218O) show the existence, in middle and high latitudes, of a linear relationship between the mean annual isotope content of precipitation (δD and δ18O) and the mean annual temperature at the precipitation site. Paleoclimatologists have used this relationship, which is particularly well obeyed over Greenland and Antarctica, to infer paleotemperatures from ice core data. There is, however, growing evidence that spatial and temporal isotope/surface temperature slopes differ, thus complicating the use of stable water isotopes as paleothermometers. In this paper we review empirical estimates of temporal slopes in polar regions and relevant information that can be inferred from isotope models: simple, Rayleigh-type distillation models and (particularly over Greenland) general circulation models (GCMs) fitted with isotope tracer diagnostics. Empirical estimates of temporal slopes appear consistently lower than present-day spatial slopes and are dependent on the timescale considered. This difference is most probably due to changes in the evaporative origins of moisture, changes in the seasonality of the precipitation, changes in the strength of the inversion layer, or some combination of these changes. Isotope models have not yet been used to evaluate the relative influences of these different factors. The apparent disagreement in the temporal and spatial slopes clearly makes calibrating the isotope paleothermometer difficult. Nevertheless, the use of a (calibrated) isotope paleothermometer appears justified; empirical estimates and most (though not all) GCM results support the practice of interpreting ice core isotope records in terms of local temperature changes.” Jouzel, J., et al. (1997), J. Geophys. Res., 102(C12), 26,471–26,487, doi:10.1029/97JC01283. [full text]

Evidence for general instability of past climate from a 250-kyr ice-core record – Dansgaard et al. (1993)“RECENT results from two ice cores drilled in central Greenland have revealed large, abrupt climate changes of at least regional extent during the late stages of the last glaciation, suggesting that climate in the North Atlantic region is able to reorganize itself rapidly, perhaps even within a few decades. Here we present a detailed stable-isotope record for the full length of the Greenland Ice-core Project Summit ice core, extending over the past 250 kyr according to a calculated timescale. We find that climate instability was not confined to the last glaciation, but appears also to have been marked during the last interglacial (as explored more fully in a companion paper) and during the previous Saale–Holstein glacial cycle. This is in contrast with the extreme stability of the Holocene, suggesting that recent climate stability may be the exception rather than the rule. The last interglacial seems to have lasted longer than is implied by the deep-sea SPECMAP record4, in agreement with other land-based observations. We suggest that climate instability in the early part of the last interglacial may have delayed the melting of the Saalean ice sheets in America and Eurasia, perhaps accounting for this discrepancy.” W. Dansgaard, S. J. Johnsen, H. B. Clausen, D. Dahl-Jensen, N. S. Gundestrup, C. U. Hammer, C. S. Hvidberg, J. P. Steffensen, A. E. Sveinbjörnsdottir, J. Jouzel & G. Bond, Nature 364, 218 – 220 (15 July 1993); doi:10.1038/364218a0. [full text]

Irregular glacial interstadials recorded in a new Greenland ice core – Johnsen & Dansgaard et al. (1992)“THE Greenland ice sheet offers the most favourable conditions in the Northern Hemisphere for obtaining high-resolution continuous time series of climate-related parameters. Profiles of 18O/<16O ratio along three previous deep Greenland ice cores seemed to reveal irregular but well-defined episodes of relatively mild climate conditions (interstadials) during the mid and late parts of the last glaciation, but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate, rather than artefacts due to disturbed stratification. Here we present results from a new deep ice core drilled at the summit of the Greenland ice sheet, where the depositional environ-ment and the flow pattern of the ice are close to ideal for core recovery and analysis. The results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt. According to a preliminary timescale based on stratigraphic studies, the interstadials lasted from 500 to 2,000 years, and their irregular occurrence suggests complexity in the behaviour of the North Atlantic ocean circulation.” S. J. Johnsen, H. B. Clausen, W. Dansgaard, K. Fuhrer, N. Gundestrup, C. U. Hammer, P. Iversen, J. Jouzel, B. Stauffer & J. P. steffensen, Nature 359, 311 – 313 (24 September 1992); doi:10.1038/359311a0. [full text]

Oxygen Isotope Profiles through the Antarctic and Greenland Ice Sheets – Johnsen & Dansgaard et al. (1972)“The Camp Century, Greenland, deep ice core reveals seasonal variations in the isotopic composition of the ice back to 8,300 years BP. This is not the case for the Byrd Station, Antarctica, deep ice core. Both cores show long-term perturbations in isotopic composition reflecting climatic changes from before the beginning of the last glaciation. But the complexity of the glaciological regime at Byrd Station precludes a rational choice of a time scale. Pole-to-pole correlations of the palaeoclimatic data therefore become speculative except for the more pronounced features and general trends.” S. J. Johnsen, W. Dansgaard, H. B. Clausen & C. C. Langway jun, Nature 235, 429 – 434 (25 February 1972); doi:10.1038/235429a0.

Climatic Oscillations 1200−2000 AD – Johnsen & Dansgaard et al. (1970)“THE idea of using the isotopic composition of glacier ice as a climatic indicator was proposed in 1954. The method is based on the fact that the concentration of heavy stable isotopes (deuterium and oxygen-18) in high polar snow increases with the temperature of formation of the snow. This causes seasonal variations in the isotopic composition of accumulated snow and ice4, as well as long-term variations due to climatic changes5. A unique possibility for studying palaeoclimates was offered when the US Army Cold Region Research and Engineering Laboratory succeeded in recovering a 1,400 metre long surface-to-bottom ice core from Camp Century on the North Greenland ice sheet. No physical dating method can be applied on the relatively small amounts of ice available, so the age of the various increments of the core had to be calculated by considering a simple ice flow model. This procedure turned out to be successful, in so far as the climate record that resulted from plotting the δ(18O) data (δ is defined as the relative deviation of the 18O/16O ratio of a sample from that of standard mean ocean water) against the calculated ages depicted known climatic events dated by other methods. In addition, unlike other methods, the stable isotope technique applied on the deep ice core gave an unbroken and detailed climatic record spanning probably 100,000 years.” S. J. Johnsen, W. Dansgaard, H. B. Clausen & C. C. Langway, Nature 227, 482 – 483 (01 August 1970); doi:10.1038/227482a0.

One Thousand Centuries of Climatic Record from Camp Century on the Greenland Ice Sheet – Dansgaard et al. (1969)“A correlation of time with depth has been evaluated for the Camp Century, Greenland, 1390 meter deep ice core. Oxygen isotopes in approximately 1600 samples throughout the core have been analyzed. Long-term variations in the isotopic composition of the ice reflect the climatic changes during the past nearly 100,000 years. Climatic oscillations with periods of 120, 940, and 13,000 years are observed.” W. Dansgaard, S. J. Johnsen, J. Møller and C. C. Langway, Jr., Science 17 October 1969, Vol. 166 no. 3903 pp. 377-380, DOI: 10.1126/science.166.3903.377.

Isotopic Distribution in a Greenland Iceberg – Dansgaard et al. (1960)“THE heavy-oxygen content in the ice of the Greenland ice cap is extremely low. This is part of a common feature showing decreasing H218O content in fresh water when going towards a colder climate.” W. Dansgaard, G. Nief & E. Roth, Nature 185, 232 (23 January 1960); doi:10.1038/185232a0.

The O18-abundance in fresh water – Dansgaard (1954)“Fresh water of various origins as distinct from ocean water shows great variations in O18-abundance. Proceeding from the temperate towards the colder climates a considerable decrease is noticeable. It is demonstrated that the O18-abundance in atmospheric water vapour is dependent on (a) the precipitation temperature, (b) the origin of the vapour and (c) the average cooling of the vapour during the circulation of the water in nature, whereas the O18-abundance in a certain precipitation, further, depends on (d) the condensation temperature, (e) the cooling since the beginning of the condensation of the vapour in question and (f) the evaporation during the fall of the precipitation from cloud to ground. Furthermore, the O18-abundance in ground water from a certain locality depends on (g) the evaporation from the precipitation since its reaching the ground and (h) the possible exchange of O18 between the water and oxygenic substances in the ground. Computations on this basis and on measurements of the O18-abundance of ocean water are in agreement with measurements of fresh water of various origins.” Willi Dansgaard, Geochimica et Cosmochimica Acta, Volume 6, Issues 5-6, December 1954, Pages 241-260, doi:10.1016/0016-7037(54)90003-4.